EEVblog #1104 - Omicron Labs Bode 100 Teardown - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: July 10, 2018, 11:16:41 pm
content: Teardown on the Omicron Labs Bode 100 Frequency Response Analyser / Vector Network Analyser

author: jbb
author_rank: Super Contributor
timestamp: July 11, 2018, 12:09:54 am
content: I guess some of the DG4xx switches are being used as precision mixers (and others used to switch filter banks etc.).It could be very interesting to (carefully!) probe the outputs of the two DDS units. I suspect that they run at different frequencies to do the heterodyne mixing. Also keep an eye out for high speed comparators to turn the sine wave frequency reference into square waves to drive switches.On the directional coupler front, I think your previous video showed a 50 Ohm series resistor with a differential amplifier across it. Maybe they’re doing electronic measurement because it would be very hard to make an RF coupler work at the lower frequency range.

author: JS
author_rank: Frequent Contributor
timestamp: July 11, 2018, 12:31:50 am
content: The reflection is easy to measure as they have access to the generators output previous to the 50Ω resistor, software is clear enough they are using that.The second dds is likely to generate the IF for the mixer, what I haven't seen is the mixer, as said the only mixy thing there are the switches but filtering that is kind of a pain, as switching mixer generates lot of side bands, should do the math for that. They could run the second dds at the same freq of the first, 90° out of phase and take down to dc in phase and cuadrature to meassure the signal, but that would take too long to settle at each step. ADC is too slow to make wide bands conversions but they are likely to still be using a fixed freq and just switch the bw of the filter. Missing a 3rd dds to make for the cuadrature reference.We have all we need to reverse engineer that transformer! Construction method, number of turns, impedance analysis, freq response... It's just matter of finding the right core material, with the impedance and number of turns permeability could be estimated... Would someone sell cores out of that material?JS

author: Wolfgang
author_rank: Super Contributor
timestamp: July 11, 2018, 01:14:25 am
content: I tried to make a modest homebrew version of this and the best solution I found for injection transformers were current transformers for AC current measurement where I added some primary windings:https://electronicprojectsforfun.wordpress.com/injection-transformers/You have to be cautious with frequency ranges advertised; these are -3dB values, and phase shift at the band corners can be too much for meaningful measurements.Another issue is the capacitance between primary and secondary. This could be way above 100pF due to the bifilar winding technique, maybe too much for some sensible circuits.

author: Bud
author_rank: Super Contributor
timestamp: July 11, 2018, 01:48:19 am
content: Quote from: JS on July 11, 2018, 12:31:50 amYou can generate quadrature LO sequentially with a single DDS as it is done in the N2PK VNA.

author: Bud
author_rank: Super Contributor
timestamp: July 11, 2018, 01:54:34 am
content: Quote from: JS on July 11, 2018, 12:31:50 amFiltering may not be needed, it depends on the architecture. VNAs are less demanding to filtering. Some, like the VNWA, dont have filtering at all. Moreover, it makes use of the aliases as the operating principle per se and to extend the bandwidth.

author: station240
author_rank: Unknown
timestamp: July 11, 2018, 02:51:36 am
content: Although it doesn't answer your question on what the wideband transformer winding style is, this page does explain why it's done that way.http://www.richieburnett.co.uk/temp/gdt/gdt1.html(unfinished page)I think the real trick is in the brown ferrite core itself, the colours denote frequency/saturation properties, I have heaps of rings but not any brown ones which I assume are RF ones.

author: Bud
author_rank: Super Contributor
timestamp: July 11, 2018, 03:09:53 am
content: Do not seem to be a RF core to me but rather a low freq material. The trick is in the bifilar coupled winding and the ransformer will work with no core at upper frequencies. The core kicks in at lower frequencies to increase the windings impedance. This is widely used in RF baluns to achieve wide frequency range.

author: JS
author_rank: Frequent Contributor
timestamp: July 11, 2018, 04:18:41 am
content: Hi, Ive done my homework and I'm back, but first.Quote from: Bud on July 11, 2018, 01:54:34 amRight, if the only thing you are interested is amplitude that's true, non linearities would be harder to pick this was as high freq harmonics will fall well beyond the ADC's bandwidth and it won't be able to determine a lot of factors. Anyway, even if filtering is done it will only catch LF harmonics and might get trickier as freq increases. I did used oversampling building something in the past, as long as you are only interested in the amplitude and missing a few narrow bands isn't a problem the only HF limiting factor is the sampling time of the sample and hold circuit. I mostly have an audio background and for HF stuff sometimes it seems more like a luggage than a background, it bites me every time.Quote from: station240 on July 11, 2018, 02:51:36 amHere is my homework, the thing seems to have39 turns40 turns, (I knew it couldn't be 39, my numbers are still with 39 but they should be pretty close anyway)if I know how to count, in the previous video we can see the impedance, 400Ω @ 300Hz means 210mH, that's AL = 140µH/N^2I estimated the size of the core, roughly a T184 core, height 18mm, outer diameter 47mm, inner diameter 25mm means a permeability of about 60000, seems like a lot but I was expecting something like that, small signal audio transformer use that kind of core permeability, low turn count low freq was asking for that, now let's look for a brown core with tens of thousands for µr... there are not that many materials in that range...I would bet it's nanopermhttps://www.magnetec.de/en/nanopermr-products/,it's the closer one I found.Here are some products,http://www.feryster.com/polski/nanoperm.php?lang=enThere's one with 40mm outside diameter, 25mm inside diameter and 15mm height, permeability of 75000, I gotchya!Oh s***t, it's blue!http://allegro.pl/rdzen-magnetec-m-083-rtn-40x25x15-nanoperm-i7430998721.htmlI don't know, I can't find the actual one, this looks like the closest, but still could work. I couldn't find a way to source the cores, always hard here in Argentina, if someone can source them would be cool to see some tests.Hf response would only depend on the parasitic inductance and capacitance, to keep inductance low they have twisted the wires, to get low capacitance low turns count and thick insulators, the tricky part is the low frequency. I do have some audio transformers I could use, they go up to tens of kHz but LF response is better than seen in the first video, having a few Henry inductance, after that a different transformer could jump in and make up for the rest of the way.@EEVblog pleeeeeeease grab some calippers and measure that core!!!JSEdited...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2018, 07:13:31 am
content: That's not ferrite and it's definitely not powdered iron, that's got to be nanocrystalline and nothing else.Most likely Vacuumschmeltze, probablyhttps://www.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2040-W453?qs=sGAEpiMZZMs2JV%252bnT%2fvX8PvC43ppqs%252bksq4V5kp6Ay4%3dor similar.Quote from: JS on July 11, 2018, 04:18:41 amNever seen any in blue, I wonder if they got them as special order, or if there's another mfg I don't know about. IIRC, it was just VAC and HMG (former Metglas) doing rapid-quench materials, but maybe there's new ones from China I don't know about?Checking, I see very little on Ali Express, so probably not.QuoteHF response is easily calculated from the transmission line length. It's a transmission line transformer, simple as that. The twisted pair will have Zo ~ 100 ohms, so that for a step input, each port of the transmission line looks like 100 ohms. That is, the equivalent circuit for short transients is:pri start -- 100 ohms -- sec start| |~open circuit ~open circuit| |pri end -- 100 ohms -- sec startThe open circuit is because the core gives the transmission line a very large common mode impedance, i.e., the two ports act as ideal ports, with no common mode connection (again, for short transients, but as it turns out, also for rather low frequencies, down to ~Hz).After one transmission line delay, the start and end waves interfere with each other, and normal transformer action is had.Note that this does NOT magically have extreme CMRR -- there's as little as 100 ohms, directly from primary to secondary (again, for short transients). At frequencies well below the electrical length, it approximates as a capacitance from each end of primary, to the respective ends of the secondary. (The exact capacitance can be calculated from line length and impedance.)Likewise, leakage inductance is the LF equivalent of transmission line inductance, and can be calculated from length and impedance.If the line is, say, 5m long (to take a ballpark guess), and vf ~ 0.8, then Cp = 208pF (total, so, say, 104pF where the 100 ohmses are indicated above), and LL = 1.67uH.Tim

author: EEVblog
author_rank: Unknown
timestamp: July 11, 2018, 07:18:39 am
content: Quote from: JS on July 11, 2018, 12:31:50 amIf you could sell a $100 unit with the same performance, you'd sell a truck load of them.Would be interesting to try and duplicate their design and what performance it has with just some random core.

author: EEVblog
author_rank: Unknown
timestamp: July 11, 2018, 07:23:13 am
content: Quote from: station240 on July 11, 2018, 02:51:36 amMany are saying it's a bifilar winding, and I actually said that in the video as my first guess, but I edited it out because I don't think it is.I thought bifilar implies same coil opposite direction and (usually?) non twisted?This one is opposite pair and twisted, totally different thing to a bifilar coil winding IMO

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2018, 07:26:40 am
content: Quote from: EEVblog on July 11, 2018, 07:23:13 amI use "bifilar" and "twisted pair" interchangeably for winding purposes.Hmm, I don't actually know if "bifilar" is, say, a brand name or something, and implies parallel wires glued together and laid flat. In any case, the characteristics will be very much the same for either method (with the twisted pair being slightly worse just due to the twist taking up some velocity factor).Tim

author: twistedresistor
author_rank: Contributor
timestamp: July 11, 2018, 07:31:39 am
content: Bifilar just means the wires are wound next to each other, regardless of the direction. The opposite would be sectional winding where the two windings are on opposite sides of the core, like seen in chokes for common mode line filters.What intrigues me the most: When i spoke to the guys at Omicron they've told me that one challenge for the transformer was that it had to be low in capacitance. But the coupling capacitance in a bifilar winding is usually higher than a sectional wound inductor.(EDIT: T3sl4co1l beat me to it. Bifilar is not a brand thing)

author: tautech
author_rank: Super Contributor
timestamp: July 11, 2018, 07:34:12 am
content: Quote from: twistedresistor on July 11, 2018, 07:31:39 amThat's as I understand it too.Twisted pairisdifferent.

author: twistedresistor
author_rank: Contributor
timestamp: July 11, 2018, 07:41:40 am
content: A twisted pair has nothing to do with winding an inductor. You can wind a twisted pair around a core - that's what they did - then you got a bifilar wound inductor.Quote from: tautech on July 11, 2018, 07:34:12 am

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2018, 07:59:20 am
content: Quote from: twistedresistor on July 11, 2018, 07:31:39 amInseparable from the nature of the transformer -- you can make bank windings, but you royally screw the leakage inductance. Basically making a very high impedance transmission line. But with a lot of self-capacitance balled up in the sections, rather than shared, so the bandwidth is awful.A typical bank wound CMC has Zo ~ 300 ohms and BW < 10MHz. Zo isn't really that much higher, because of the self-capacitance.This TLT will have BW out until TL effects cause peaks and notches; these are dampened when Zin and Zout are matched, i.e., 100 ohm source and load. At 50 ohms, the peaking will be noticeable, and the cutoff will be a bit worse (about 1/2 bandwidth).Incidentally, the rolloff will NOT be that silky smooth curve they showed. You can see this in CMC datasheets, the ones that are bifilar wound (data chokes), there are multiple peaks and valleys in the diff mode response, because the measurement is made as a shorted transmission line. That it has peaks, means your data will propagate safely all the way up there.(For common mode, that is. For isolation mode, there are peaks.)Tim

author: Kleinstein
author_rank: Super Contributor
timestamp: July 11, 2018, 08:20:56 am
content: Quote from: Bud on July 11, 2018, 01:48:19 amThere is no need for a quadrature LO if the ADC is not seeing zero IF, but more like an IF in the audio band. The 2 nd DDS would than be the LO, slightly offset from the output frequency. The quadrature part is than at the second virtual IF done in software. So to a good part this is very similar to the simple SDR receivers. It is kind of doing the quadrature at a different time though more continuous phase shift instead of switching between 2 cases.As the LO is used to drive CMOS switches as mixers, there would be digital LO signal and thus no problem generating quadrature signals with 2 D flip-flops and running the DDS at twice the LO. Still the ADC seems to be single channel only - so this way is likely not used, though it might offer slightly lower noise.I would guess the FPGA might have enough processing power to do the IF processing and thus much less data transferred via USB. Using an FTDI USB chip also points to a rather low data rate.

author: JS
author_rank: Frequent Contributor
timestamp: July 11, 2018, 08:37:37 am
content: Quote from: EEVblog on July 11, 2018, 07:18:39 amI could certainly try, at least that would justify buying a decent freq gen for the lab. Could you measure the core size for me? First out would certainly be a mailbag for the EEV!Quote from: T3sl4co1l on July 11, 2018, 07:13:31 amThat's for sure, the banner picture on the ones I posted had blue and brown cores, the ones I found for sale with the part numbers I was looking shown blue pictures but that's the only reference I got and I can't even read the web in that language!QuoteI would guess under 3m, 10MHz wavelength is 30m, about 20m inside the wire, so transmission line is not quite needed in this case, I think concentrated parameters should get to a reasonable guesstimate. Also, in the first video, HF impedance looks capacitive, which makes sense for me I guess. I didn't took the time to look for looking at HF as I was trying to get the core parameters.Here is the plothttps://youtu.be/66s9easZKxU?t=35m42sThe plot shows 200Ω at 1MHz, that's about 800pF. That's in the ball park from 100kMHz to 7MHz. It looks too high to me but still being a lot of things around, which will be used with this transformer anyway, still looking pretty high... Phase is over 70º and parallel resistance looks like 2k so I don't know why such a high capactance, I could bet it's not from the winding. I've wound a few transformers and with a few hundred turns of enamel coated wire around a chunk of iron, trifilar wound, got about 5nF. This has shorter 40 turns of polymer insulated wire, not teflon, the solder melted a little of it...Then a bit over 10MHz there is a resonation, that might be inductance of wires going to the transformer, after that it start to behaves as you see and there might be due to the wavelength getting closer to the winding length.Quote from: twistedresistor on July 11, 2018, 07:31:39 amThe capacitance they needed to make low is probably the equivalent parallel capacitance of the secondary (refered to the secondary as it will act as a 2nd order LPF there together with the leakage inductance. I'm considering concentrated parameters, not transmission lines, but we are in a middle ground here at 10MHz. As said twisted wires gives the lower leakage inductance which is a very good thing for HF transformers.Quote from: Kleinstein on July 11, 2018, 08:20:56 amThis post is getting long, as I write I receive more answers... ADC could still be multiplexed, time difference between corrected in DSP, as long as IF is low enough. I was expecting a balanced mixer making filtering easier, but we are in a digital world so digital it is, there was a 595 somewhere in there, so...For the times it takes to the software to load a different measurement mode and the real time data plot, I would guess you are right about processing in the FPGA, if it would be just pushing data via USB there's nothing to load other than a different algorithm to ram, which I'd expect to be quicker load times, slower plotting.JS

author: Wolfgang
author_rank: Super Contributor
timestamp: July 11, 2018, 10:09:46 am
content: I would say the big difference between bifilar and twisted bifilar is better coupling and a better controllable transmission line impedance for the twisted bifilar case.This thing is definitely a transmission line transformer using a very high mu core.Useful information about transmission line transformers and their construction can be found in the "Transmission Line Transformers" Bible by Jerry Sevick.

author: Bud
author_rank: Super Contributor
timestamp: July 11, 2018, 11:43:45 am
content: It is not a transmission line transformer. You cant excite opposite ends of a transmission line and call it TLT just because you used a transmission line for it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2018, 12:32:41 pm
content: Quote from: Bud on July 11, 2018, 11:43:45 amSo then what is it?Transmission lines are a superset of whatever you think "transformers" are; it's well worth learning, both for understanding their use, and creating their design.Tim

author: Bud
author_rank: Super Contributor
timestamp: July 11, 2018, 12:51:37 pm
content: of course Tim it worth learning, so feel free to pick up ANY book on TL and start reading transmission line theory.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 11, 2018, 02:07:56 pm
content: Who on earth can stop me doing exactly that ?Whats wrong calling a transformer made from transmission lines a transmission line transformer, independent of the the circuit that it is embedded into ?Confusing ...

author: Floyo
author_rank: Regular Contributor
timestamp: July 11, 2018, 04:49:07 pm
content: On the diy front there is some more info to be found here:https://www.eevblog.com/forum/projects/diy-injection-transformer-for-power-supply-control-loop-response-measurements/There I attempted one version of an injection transformer, but this teardown made me try something more akin to the Omicron setup.I took a magnetec M-012 Nanoperm core and wound around 50 turns of thin 50 ohm coax onto it, the "shield" is the primary, and the inner conductor the secondary. Attached are the measurements with the Analog discovery. Test were done with a 47 and 1K2 ohm load resistor on the secondary side. Drive impedance from the analog discovery wavegen was switched from 50 to "0" ohms, the latter increases the low frequency amplitude. Primary inductance is 72mH and pri-sec capacitance is 400pF.Results look quite ok for just slapping some turns on a core. Keep in mind that the power supply injection measurements are relative to the secondary, so absolute amplitude and phase of the transformer doesn't matter too much, if its decently well behaved.

author: DutchGert
author_rank: Frequent Contributor
timestamp: July 11, 2018, 04:54:27 pm
content: Hmm, am I the only one that is not impressed at all by the PCB layout job done?The DC-DC convertors are done sloppy (big loops, small traces etc).TH electrolitic caps everywhere, what about SMT MLCC's or Polymer jobbies?Power is routed with thick traces, what about a nice solid power plane(s)?

author: dardosordi
author_rank: Regular Contributor
timestamp: July 11, 2018, 05:27:59 pm
content: Im sure they regret not having potted the transformer now...

author: PA4TIM
author_rank: Super Contributor
timestamp: July 11, 2018, 05:31:06 pm
content: I just thinking, the output and input of the instrument are single ended and both connected to the same ground. The transformer is balanced. I have no experience with this kind a measurements but if you use it to isolate the DUT from the analyser then you need two of them for 2 port measurements. One on the input and one on the output.I think you must connect it between two baluns to measure how it behaves for real isolation.

author: rx8pilot
author_rank: Super Contributor
timestamp: July 11, 2018, 05:38:55 pm
content: Quote from: dardosordi on July 11, 2018, 05:27:59 pmI doubt it....their customer base is probably very unlikely to bother making their own transformer. As much as I like to save money, spending a few days and at least a couple hundred $$ on failed attempts is a terrible way to 'save' $500.For those looking for a bargain price, they were never going to be a viable customer anyway.

author: rx8pilot
author_rank: Super Contributor
timestamp: July 11, 2018, 05:40:10 pm
content: Quote from: rx8pilot on July 11, 2018, 05:38:55 pm

author: Wolfram
author_rank: Frequent Contributor
timestamp: July 11, 2018, 07:53:15 pm
content: Quote from: T3sl4co1l on July 11, 2018, 07:13:31 amAt PCIM this year, Tamura was presenting nanocrystalline CMCs, so they might also have the capability.Quote from: JS on July 11, 2018, 08:37:37 amI can confirm that the Vacuumschmelze nanocrystalline cores are the same color as the core in the EEVBlog video.

author: AndersJ
author_rank: Frequent Contributor
timestamp: July 11, 2018, 08:09:55 pm
content: When the transformer secondary is connected to the DUT,it will most likely cause a short circuit.Why is there no coupling cap in the box?

author: Wolfram
author_rank: Frequent Contributor
timestamp: July 11, 2018, 08:14:40 pm
content: Quote from: AndersJ on July 11, 2018, 08:09:55 pmAn injection transformer like this is not connected to the output of a power supply, it is inserted in series with the feedback loop (across a resistor). See the drawing in the user manual for clarification:https://www.omicron-lab.com/fileadmin/assets/Bode_100/Accessories/B-WIT_100/B-WIT-B-LFT-User-Manual-V1.1.pdf

author: Wolfgang
author_rank: Super Contributor
timestamp: July 11, 2018, 08:26:20 pm
content: It goes into the cut open feedback loop, not parallel to the load. What you are thinking of is a current injector. The Omicron people also have those.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2018, 02:14:17 am
content: Quote from: PA4TIM on July 11, 2018, 05:31:06 pmQuite right, you only get good CMRR when the transformer is used in balanced operation, and the source and load are understood to have perfect CMRR.Unbalanced, you get full capacitance (at medium frequencies, until it becomes obviously transmission line based in the HF limit).The trick is to put a CMC on both sides of the transformer, to restore CMRR in the MF to HF limit. Note that the CMC inductance resonates with the isolation capacitance, so it should be chosen (lossy material, or R+C in parallel) such that the resonance is well damped. CMCs can be stacked (given the same consideration) to extend the CMRR arbitrarily.Tim

author: Wolfgang
author_rank: Super Contributor
timestamp: July 12, 2018, 10:32:22 am
content: Theoretically, this is all correct. In practice, I personally have never seen any documentation or video using two isolation transformers or common mode chokes.Do you have a working example of this somewhere on the web ?

author: JS
author_rank: Frequent Contributor
timestamp: July 12, 2018, 01:25:24 pm
content: Quote from: EEVblog on July 11, 2018, 07:18:39 amForgot to answe this, it will result in a poor LF reaponse, depending on the core permeability, bassicaly the prinary inductance and the 50Ω makes a HPF which limits that, but even over that freq there is some distortion due to magnetization hysteresis which tapers off to the transformers higher freqs.Please dave, when you find yourself on the lab with a screw driver and some length measurement device can you take a look at the core? To aim for a similar freq range that's kind of a big deal and I can't start making prototypes to shoot for one, sourcing those cores in Argentina is kind of tricky, as almost any component other than a 2n3904...JS

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2018, 03:09:23 pm
content: Quote from: Wolfgang on July 12, 2018, 10:32:22 amIn fact it is out there in the wild -- you're probably using it right now, though you may not have seen or noticed it! Example:https://www.mouser.com/datasheet/2/336/H329-1199189.pdfTim

author: envisionelec
author_rank: Frequent Contributor
timestamp: July 12, 2018, 05:39:00 pm
content: I reverse engineered the entire design and ran a cost analysis on a 10 piece basis.The BOM cost is 110.84 including nominal labor/machining fees.That's PTFE coated wire - 1USD a foot and there is about 24USD worth of wire on that core. I'll build one and characterize it.

author: rx8pilot
author_rank: Super Contributor
timestamp: July 12, 2018, 05:43:51 pm
content: Quote from: envisionelec on July 12, 2018, 05:39:00 pmIf that is correct.....the $500 price tag is a bargain for such a specialty/low volume piece of gear.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 12, 2018, 11:19:43 pm
content: Well, I never saw them in a *measurement* application like Bode plotting or LF VNA. Any use there I missed ?

author: JS
author_rank: Frequent Contributor
timestamp: July 13, 2018, 12:01:43 am
content: Quote from: envisionelec on July 12, 2018, 05:39:00 pmWhat tells you it's PTFE? I see some deformation of the insulatoe on the BNC solder, that shouldn't happen with PTFE...For running small batches I could machine those my self and all labor so all that would come to my pocket but I'm trying to find the customs fees for importing the cores and then exporting the devices, that could ruin my budget to sell them at any reasonable price...I intend to order a few cores to test and see what happens, worst case I end with an injection transforner for myself and a few nice cores for other applications, I probably will find them useful in audio, but before they arrive I could make some with any cheap core and look at the HF response where permeability doesn't play a big role. LF response will be anything but nice, I know that.JS

author: Wolfgang
author_rank: Super Contributor
timestamp: July 13, 2018, 01:26:28 am
content: Of course you could try to reproduce the omicron injection transformer 1:1.An alternative could be to use a stock ISDN or current transformer and to add a damping/compensation network to flatten out amplitude and phase response. Most swept generators have by far enough output for this approach, and the injected stimulus voltages are normally very small in order not to overdrive the DUT. When I tried this and if you apply the same criteria (5% phase error), results are not so vastly different from what omicron offers (e.g. 100Hz to a few 100kHz). The omicron claim of 1Hz to 10MHz is pure marketing; at band corners they are 15dB down and have phase errors of 70°. If you apply 1dB amplitude and 5°C phase error criteria, the range for them is ca. 50Hz to a few 100kHz (information from the datasheet of the B-WIT100). The big difference is that you have a 40dB power attenuation for the homebrew approach, which does not hurt at all in most cases.https://electronicprojectsforfun.wordpress.com/injection-transformers/

author: rx8pilot
author_rank: Super Contributor
timestamp: July 13, 2018, 01:45:44 am
content: Quote from: Wolfgang on July 13, 2018, 01:26:28 amThey compensate in the box/software but print the spec on the box - making it look like is wider than anyone else would claim. Since it is a closed system, it's only sorta cheating.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 13, 2018, 01:58:35 am
content: I see it the same way, its marketing. Of course you can calibrate this out, but you could do the same with a homebrew probe. The homebrew has further advantages (4kV isolation voltage plus less capacitance). I wonder why Dave was so impressed by this transformer.

author: JS
author_rank: Frequent Contributor
timestamp: July 13, 2018, 02:14:51 am
content: Quote from: Wolfgang on July 13, 2018, 01:26:28 amI like my phases in ºK, as ºC aren't absolute...QuoteOne could also make a current amplifier and build a current transformer for the same freq range which might be easier, LF in current mode is much more forgiving than voltage mode, then terminate the transformer with the proper resistor and go from there. All that seems fine for the average lab, but this transformers exists for a reason, also, 1:1 transformer have betterThis is from a transformer I've built some years ago for audio applications, source impedance was low, like 10Ω at most. The wiggle in the top end is due to the sound card I used, not coming from the transformer, I wander how it keeps going to a higher frequency, I only got the sound card at the time, so not much over 20kHz to work with at the time but I still have some of those at home, I'd only expect to get to a few tens kHz, is a big chunk of iron with a lot of turns, but I could wind a smaller one with less turns and better insulated wire to try.Quote from: Wolfgang on July 13, 2018, 01:58:35 amIt's specs aren't 1Hz to 10MHz, at least not in Dave's measurement, 5º was happening around 1.5MHz but at 1Hz was only 3º out. Test setup can influence on the measurement but his were at least as clean as you will get in a measurement setup. You don't need more than that, you need smooth transfer function without too much attenuation, as you can pick the reference from the output of the transformer, maybe a 3rd coil could be useful for that as it will reflect what the output is putting out better than the input coil and you wouldn't need a differential probe. In any case I wouldn't trust that what the generator is sending is the same as what the device is getting.JS

author: chris_leyson
author_rank: Super Contributor
timestamp: July 13, 2018, 02:28:51 am
content: The core in the injection transformer is probably some nanocrystalline material as T3sl4co1l pointed out. It's got to be to get the high permiability required to get high magnetising inductance at low frequency. As it's a wideband transformer the low frequency limit is defined by the allowable peak flux density. From the data sheet fig. 5-2 they recommend a maximum drive level of 10dBm at 10Hz assuming a 10ohm injection resistor.So, 10dBm is 0.707V RMS into 50 ohms or 1.414V RMS open circuit voltage at the generator output. Assume load resistance is 10 Ohms so that gives you 1.414*10/(50+10) or 235mV RMS across the primary. Peak flux density from the transformer equation is Bpeak(T) = Erms/(4.44 * f * N * Ae). N = 40, f = 10Hz, lets be generous and say Ae is 3cm2= 3x10-4m2putting the numbers in gives about 440mT peak at 10Hz. Also in the data sheet they give peak flux density as a volt time product, 3.5E-3 Vs, assuming 3cm2that gives a peak flux density of around 300mT. In calculating the RMS primary voltage I left out the primary magnetizing inductance and that would reduce the primary RMS voltage a little bit. It seems like quite a high working flux density, compared to ferrite anyway. It's only just about useable at 10Hz and I would say "usable at 1Hz" is pushing it a bitBifilar literally means "two filiaments" and it's two parallel wires bonded together, I've got a reel of it somewhere for winding coupling transformers on tiny binocular cores. Scientific wire company sell ithttps://www.scientificwire.com/acatalog/bifilar.htmlThe winding on the toroidal core is twisted to probably reduce the electric coupling between adjacent turns, MiniCircuits for example wind coupling and matching transformers using twisted wire.Where are the mixers ? They're probably using analog switches, cheap, wide dynamic range and poor noise figure.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 13, 2018, 07:26:58 am
content: The advantage of the nano-crystalline core material is that is can be used to higher flux levels than ferrites. So 400 mT would be no problem. When used in mains transformers some 800-1000 mT should be OK, saturation is around 1.1-1.2 T.At low frequency the maximum power gets lower and the impedance gets lower. Still injecting 0.1 V might still be enough.From the other tread (EEV-blog 1103): Dave showed a picture with an AD834 that is likely used as the mixer.

author: JS
author_rank: Frequent Contributor
timestamp: July 13, 2018, 08:49:50 am
content: So switches aren't used for the mixer, autocal, signal routing and filter managment I guess, there where a lot of them, I should take a look for the high res pictures!JS

author: Wolfgang
author_rank: Super Contributor
timestamp: July 13, 2018, 10:33:58 am
content: Quote from: JS on July 13, 2018, 02:14:51 amStill a big discrepancy to their own datasheet. I need to research this a little bit. I am afraid I need to get hold of a Keysight E5061B with LF option

author: EEVblog
author_rank: Unknown
timestamp: July 13, 2018, 11:13:46 am
content: It looks like they take +/-40deg as the "frequency range" of the unit (i.e. 7Hz to 5MHz).The 1Hz to 10MHz is the "usable range"

author: EEVblog
author_rank: Unknown
timestamp: July 13, 2018, 11:14:53 am
content: Quote from: Wolfgang on July 13, 2018, 01:58:35 amIt's a heck of a lot better than some DIY ones I've used.

author: Hydron
author_rank: Super Contributor
timestamp: July 13, 2018, 11:28:54 am
content: Dave, could you quickly check the magnetising inductance of the isolation transformer? Would help with understanding what the low frequency performance is actually like.If you wanted to go to town and play with the new toy then feel free to do a full set of measurements of the parasitics - the VNA (aka FRA) is great for this. Definitely agree that an instrument like this is very handy to have around - you'll keep finding uses for it.Edit: Just found the SPICE model on their website - no need to measure it unless you want to compare specs to reality.

author: bitwelder
author_rank: Super Contributor
timestamp: July 13, 2018, 11:58:56 am
content: For 5K I'd hoped Omicron' virgins would have taken care to align those relays a little better.

author: Wolfgang
author_rank: Super Contributor
timestamp: July 13, 2018, 12:53:22 pm
content: @DaveWhy didnt you use a matching network to straighten things out ?BTW: In about 2 months Im getting my hands on a Keysight E5061B-3L5 (5Hz to 3GHz) VNA with impedance measurement option.Then I can repeat my measurements, and I will publish them as usual.regardsWolfgang

author: Wolfgang
author_rank: Super Contributor
timestamp: July 13, 2018, 01:50:39 pm
content: Omicrons nude virgins definitely work in the software department

author: envisionelec
author_rank: Frequent Contributor
timestamp: July 13, 2018, 01:59:55 pm
content: Quote from: JS on July 13, 2018, 12:01:43 amThe pattern of deformation is exactly what PTFE looks like when its heated. Soldering that center pin takes a lot of heat...The core isn't anything special either. I'd be willing to bet it's a bog standard iron powder T184-2. Just a hunch.

author: Floyo
author_rank: Regular Contributor
timestamp: July 13, 2018, 06:47:01 pm
content: It cant be that T184-2 core, the AL is way too low to get the specified inductance. My bet goes out to a Vacuumschmelze W424, the colour matches, the size matches, as do the specs if you run the numbers. I knew I had one of those laying around somewhere, so I dug it up and whipped up another test. This time 50 turns (I had some wire leftover after 40) on the W424 core, the picture speaks for itself.Once again I measured with the analog discovery. The "Cal" image shows the wavegen output connected to both CH1 and CH2.CH2 is displayed in blue and is in relative mode, so gain and phase relative to channel one. This removes any gain variations due to wavegen output loading etc (its a 50 ohm output)."Abs" shows the measurement as Omicron does it, I think, Here the amplitude is absolute compared to the wavegen (and thus -6db because of the 50Ohm termination), and the phase is relative to CH1."Rel" is the same measurement, but now in relative mode, this shows the transfer function of just the transformer."100mV" is the previous absolute measurement but now at 100mV instead of 1V input amplitude, this lessens the loading on the wavegen output stage.Pri -sec capacitance is 130pFMagnetizing inductance is 274mHAnd leakage inductance is 3uH

author: rx8pilot
author_rank: Super Contributor
timestamp: July 13, 2018, 07:07:16 pm
content: What influence does the twist pitch of the wire have on performance?

author: Wolfgang
author_rank: Super Contributor
timestamp: July 13, 2018, 07:19:46 pm
content: It changes the characteristic impedance of the transmission line. Depending on twists/m, the impedance will be around 100Ohms, with more twists making the impedance lower.Its not extra simple, because wire diameter and dielectric used also play a role.

author: Floyo
author_rank: Regular Contributor
timestamp: July 13, 2018, 07:33:52 pm
content: How about using coax, it has already been tuned to be a good 50 ohm transmission line. And how about impedance matching from primary to secondary, and/or the transmission line impedance.For practical measurements on power supplies etc 1-2 Mhz should be plenty of bandwidth. I have never seen anything that comes close to those bandwidths, but you never know

author: GigaJoe
author_rank: Frequent Contributor
timestamp: July 13, 2018, 07:56:02 pm
content: it seems close , Vitroperm 500 F , Vacuumschmelzehttps://www.mouser.com/pdfdocs/VACChokesandCoresDatasheet.pdf

author: Hydron
author_rank: Super Contributor
timestamp: July 13, 2018, 11:02:40 pm
content: Damn, just went to post my DIY effort and found I'd been beaten to it!I too used a nanocrystaline core, this one scavenged from a Wurth 3-ph CM choke:https://katalog.we-online.com/pbs/datasheet/744839047160.pdfLooks to be a little bigger than the one linked earlier, and encapsulated inside a plastic shell (I removed the protrusions in the pic before winding it).Made a twisted pair with a drill and some random hookup wire and put 40 turns on it, as this coincidentally both matched the original number and also gave the same magnetising inductance as the SPICE model of the original indicated (actually 39 would have been the correct number in restrospect).Took maybe an hour all up to build (not including measurements) and gave:Xm = 222mHXl (per winding) = 1.25uHCpri-sec = 140pFUnfortunately I couldn't do the whole sweep from 1Hz-10MHz in one hit, so there are four graphs here (corresponding to Floyo's "abs" and "rel" measurements - filenames should be descriptive enough of what's being measured).While the low-freq performance of mine is slightly better, it only makes it to ~7MHz before falling apart. Possibly because I wound it while clothed, and don't fulfil the other two criteria either?

author: JS
author_rank: Frequent Contributor
timestamp: July 14, 2018, 04:11:48 am
content: Quote from: Hydron on July 13, 2018, 11:02:40 pmNice attempt, I like the response, being bigger might give you the good LF response. The plastic shell leaves the wire further away from the core, making a worse coupling thus higher leakage inductance which could affect the HF inductance. Also, the non PTFE wire would affect HF performance, I guess one or both of those are giving you the differences. You could try twisting the wires a bit more or building a thiner shell for the core (like some tape to keep it together and not damage the wire insulator) if you are after a better HF response.I'd love to have some cores to play around with!JS

author: chris_leyson
author_rank: Super Contributor
timestamp: July 14, 2018, 06:53:01 am
content: Big thanks to Tim for the heads up on Vacuumschmelze nanocrystaline material. T60006-L2040-W424 looks like the core they use, it's got the right Al value. Thanks to Floyo and Hydron for winding some test transformers and providing test results.I wonder, did Omicron try 2:1 and 3:1 transformer ratios if they are injecting voltage into a 10 Ohm load. Why would you pick 10 Ohms and not 50 Ohms for a load anyway, it doesn't make any sense. Twisted trifilar or quadrifilar wound would give you the impedance match either side of 10 Ohms and also drop the LF corner. Not sure how that would effect the HF corner, will have to try it out. Nice 1:1 wideband transformer, no magic voodo involved and overpriced for what it is. More marketing than practical engineering.Anyways, thanks Tim for the heads up on the material, it's not cheap and won't compete with ferrite in terms of price but for wideband transformers it has potential, all depends on the HF losses.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 14, 2018, 08:10:13 am
content: Cheers.Note that you can use ferrite just fine, but you'll lose a couple octaves at the low end. You can find materials with mu_r up to about 20k, with >8k being typical for hi-mu types.The mid-band (i.e., magnetizing) impedance also isn't as high, but this isn't relevant at these impedances. It's quite useful for CMCs, hence the application of nanocrystalline material there as well.Tim

author: Hydron
author_rank: Super Contributor
timestamp: July 14, 2018, 08:56:39 am
content: I took some 50 ohm load measurements at the same time if they are of interest - see attachments.As for PTFE vs PVC wire, I didn't have any of the former, though I could butcher an Ethernet cable for a pair of something which I assume is not very lossy. Would it really make a major difference at <10MHz? Throwing my measured lumped parameters into SPICE gives reasonable correlation to the measurements (biggest outlier is that the resonance point in SPICE is a little higher - more like 8.5MHz than ~7MHz).There are also some other things I could do to improve matters if I ever needed to use this in anger up near the top of it's range - a few less turns, shorter lead-in wires etc etc. No real need though, this was mainly done for the challenge (wasn't much of one given the right core material) and I already have an isolated sig-gen for my Cleverscope which lets you do the PSU loop measurements from <1Hz up to 65MHz with no magnetics required.

author: capt bullshot
author_rank: Super Contributor
timestamp: July 23, 2018, 08:13:24 pm
content: Building a transmission line transformer like this appears quite a challenge ...Anyway, here's my results (using random cores from the junk box, didn't record the µH/n² values):The ugly, a rather bulky ferrite core and thin litz wire (about 5m wire length)Works (-3dB) from 81Hz to 3.4MHzNext try, a core used as an EMC suppressor (just a multi-strand cable fed through it), and Wire-Wrap (ca. 3m)-3dB from 117Hz to 11MhzA core scavenged from an EMC common mode choke (VAC / Sekels branded, rather small), used less than 2m twisted pair from a CAT5e ethernet cable-3dB from 48hz to 14MhzNow I'm searching for a somewhat larger core of the last kind (probably micro-crystalline, as it is from VAC/Sekels) to give it another try and reach lower frequencies. The length of the twisted pair clearly defines the upper limit, simply verified by measuring a length of twisted pair before winding it onto the core.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 23, 2018, 09:05:17 pm
content: There are 2 effects limiting the usefulness at low frequency:1) core saturation, which is amplitude (voltage) dependent2) the inductance and thus impedance, which would depend also on the source / load impedanceWith the high Al ferrite cores, it can be important to keep the mechanical stress from the windings low (e.g. add so foam). Stress can lower the AL value quite a lot.The nano-crystalline material, has low magnetostriction and is thus less sensitive to stress.Magnetostriction also causes another effect (ferro-resonance):there can be a rather narrow mechanical resonances (high Q, maybe 1000) that can also act back on the electric parameters. Due to the small width it could be easily overlooked. For high quality it might help to have some soft (e.g. wax) potting of the transformer / winding to dampen the resonances.

author: halexa
author_rank: Regular Contributor
timestamp: July 23, 2018, 09:08:03 pm
content: Why is there no ground fill ont that main PCB?

author: rx8pilot
author_rank: Super Contributor
timestamp: July 23, 2018, 10:14:00 pm
content: Quote from: capt bullshot on July 23, 2018, 08:13:24 pmI would be rather happy with that one in many applications.Is that a 3577A you used for the test?

author: thm_w
author_rank: Super Contributor
timestamp: July 23, 2018, 11:00:08 pm
content: Quote from: halexa on July 23, 2018, 09:08:03 pmYou'd have to ask the designer. But there would be at least a few inner planes (4+ layer PCB), used for power and ground.So strictly there is no need for a top layer ground fill, but could reduce EMI slightly if it were used.

author: capt bullshot
author_rank: Super Contributor
timestamp: July 24, 2018, 05:37:33 am
content: Quote from: rx8pilot on July 23, 2018, 10:14:00 pmIt's easy to build, I'll try to find the original part number of the core / EMC choke, and I'm going to look for more cores / chokes when I have some spare time, visiting the various junk boxes (including the new stock, that isn't junk at all).QuoteYes, it is mine. Located in my home lab, we don't have such fancy stuff at work, but quite a variety of EMC chokes ...

author: capt bullshot
author_rank: Super Contributor
timestamp: July 24, 2018, 12:03:15 pm
content: Just for the record, the core I've used for the third transformer is most probably the Vacuumschmelze T60006-L2030-W423, this is the nearest match. The common mode choke that I scavenged that core from is a T60405-R6166-X018-80. Didn't find any more interesting cores for more experiments. Can't beat the mentioned T60006-L2040-W424 with any of the cores that I've found.

author: rx8pilot
author_rank: Super Contributor
timestamp: July 24, 2018, 04:30:42 pm
content: Quote from: capt bullshot on July 24, 2018, 05:37:33 amFor this thread - I was setting up to do some tests with the same 3577A network analyzer unit. The PSU has some issues and it finally would not power up at all. I believe I have located the problem and parts are on the way. Hopefully, if the failed PSU did not fry the rest of the system, I can do a few tests as well.I have 3 DC-DC converters on the design table and would really like to improve my ability to analyze loop stability.

author: precaud
author_rank: Frequent Contributor
timestamp: July 25, 2018, 02:21:07 pm
content: All this good transformer work really should be moved to its own thread in an appropriate forum...

author: capt bullshot
author_rank: Super Contributor
timestamp: July 25, 2018, 06:55:50 pm
content: Made another two transformers using that salvaged VAC core. Used bifilar (non-twisted) winding, PTFE isolated.Results1st one made with one layer of turns, resulting in about 30 turns, the core has 62µH/n²-3dB response is from 71Hz to 14MHz, one can see about 0.2dB transmission loss.The former one that was wound using twisted pair from ethernet cable has near zero losses, so I believe these losses are due to the wire's resistance.2nd one made with two layers of turns, about four times the magnetizing inductance, resulting in-3dB response from 19Hz to 8.4MHz, somewhat more loss, maybe 0.3dB. It's not exactly a fourth of the 1st ones LF response, this is because I cut the wire somewhat too short, wasn't enough for 60 turns.And now for something completely different:I've connected them to the TDR to measure the wire length and see the transmission line's impedance:Todays 1st one:Todays 2nd:And for comparison, this one from last week to point out the difference between bifilar and twisted pair winding:One can clearly see, the impedance over wire length is flatter for the twisted pair, but it appears to have none or very little effect on the frequency response.

author: rx8pilot
author_rank: Super Contributor
timestamp: July 28, 2018, 01:12:58 am
content: Quote from: capt bullshot on July 25, 2018, 06:55:50 pmI just got my 3577A repaired.....just trying to figure how it works now. So far, I have not actually used it.......I have some transformers and parts to take a shot at this but need to make sure I am setting up the test correctly.

author: capt bullshot
author_rank: Super Contributor
timestamp: July 28, 2018, 07:19:17 am
content: I've made these measurements with the transformer terminated by the 50Ohm input. Switching the input to high impedance and using an 10Ohm resistor to terminate the transformer gives different results. The low -3dB is shifted down to below 10Hz with the second transformer, the upper end -3dB gets about 7MHz.Don't forget to normalize the 3577A (with no transformer, but termination as wanted). I've used log sweep from 5Hz to 20Mhz , 120s (or 60s) sweep time and 1Hz RBW, auto RBW off.I've made this simple test rig, the switches are used to bypass the DUT, one can see the 10Ohm termination resistor placed into the pin sockets. The upper left SMB connector isn't used for anything, just in case you wonder.

author: DualTriode
author_rank: Contributor
timestamp: July 30, 2018, 02:17:31 am
content: Hello,My first post here.California is on fire, when the smoke clears I will test this thing.The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.https://www.mouser.com/datasheet/2/599/W514-238036.pdfSee the attached photo of the real deal side by side with a home rolled version. The home rolled version has 40 turns of twisted pair CAT 6 plenum wire.Thanks DT

author: Hydron
author_rank: Super Contributor
timestamp: July 30, 2018, 09:11:34 am
content: Nice, looks like the closest match yet (physically at least)!Seems that Dave's "Nude Austrian virgins" line suckered a bunch of us into proving him wrongTo be fair it is a relatively exotic core material.

author: precaud
author_rank: Frequent Contributor
timestamp: August 01, 2018, 04:56:11 pm
content: I thought it might be useful context to show what 50-Ohm isolation xfrms are available on the used market for relatively little money.Here are the plots of two North Hills 50-Ohm Isolation Transformers, models 0016 PA and 0017 CC. They have been around for more than 20 years, and the latter has been on HP/Agilent's recommended list for about that long. I don't know why HP never mentioned the 0016, because its the better. These measurements are made with 50 Ohm source and termination, into 1M inputs. The Anritsu VNA only goes down to 10Hz so a separate measurement was made down to 1Hz.As you can see, both units have very good LF extension, less than -3dB down @ 1 Hz. Reducing the source impedance extends it further. On the high end, the 0016 is -3dB at about 24MHz and the 0017 to 7.5MHz. Response shape above a few MHz is greatly impacted by analyzer input and cable reactances. Best plan is to terminate the xfmr right at the secondary output.These things generally go for 30-60 bucks when they show up on eBay.

author: DualTriode
author_rank: Contributor
timestamp: August 02, 2018, 03:55:22 am
content: Hello,Went out through the wild fire smoke to the shop.I tested both the real B-WIT injection transformer and the Home-Roll.Pretty much Same Same.Thanks DT

author: precaud
author_rank: Frequent Contributor
timestamp: August 02, 2018, 04:04:39 am
content: Thanks for posting this. Not much different from the NH 0016 tested above.

author: ace1903
author_rank: Regular Contributor
timestamp: August 02, 2018, 09:15:18 am
content: There is cheap source of vitroperm cores in RCD switches. I took one from hardware store for ~10eur.Obviously it is smaller when compared with "original" one. Don't know if 300mA has bigger core.Anyone interested to make measurement and compare results?I have LCR meter but don't have network analyser.Attached picture of RCD Commel 470-025 with core opened from protective plastic.

author: capt bullshot
author_rank: Super Contributor
timestamp: August 02, 2018, 09:58:41 am
content: You could measure the inductance of one turn.This value should be larger than 60uH to make the core interesting, I've also had tested some cores with 20uH / n^2, they didn't give satisfactory results (too many turns required for the low frequency rolloff, killing the high frequency response).

author: ace1903
author_rank: Regular Contributor
timestamp: August 02, 2018, 10:48:43 am
content: Measured with Voltcraft LCR-300 single turn:88uH at 100Hz Q2.6287uH at 120Hz Q 2.9279uH at 1kHz Q4.6246.6uH at 10kHz Q1.6428.46uH at 100kHz Q0.668Is this drop at 100kHz expected? I mostly do embedded programming and digital electronics and I maybe did some error during measurement( with 8 turns results are similar with more drastic drop).I also own Analog Discovery 1 and probably can do some kind of transfer characteristic measurement but I lack knowable how to make measurement set up.Where to put resistors and with which value?

author: capt bullshot
author_rank: Super Contributor
timestamp: August 02, 2018, 01:31:13 pm
content: Yes, that drop in inductance is to be expected for that kind of core.If you manage to apply 40 ... 50 turns of twisted pair or bifilar as done before here in this thread, I'd expect a pretty low frequency limit for it. Upper limit depends on the length of wire, try not to get longer than 2 ... 3 meter.So, now take the wires of same colour as input / output of this transformer, you should measure (number of turns)^2 * 79uH @ 1kHz as the magnetizing inductance at either input and output. Short output and measure the inductance of input, you get the stray inductance, that should be pretty low for this construction.Next apply a function generator at the input, connect a 10 Ohm resistor across the output and measure voltage across that output. Sweep frequency from 1Hz (or whatever is lowest possible) to 20Mhz at a rather low level (< 1Vpp) and draw the frequency response (bode plot). This should get similar results to the posted plots. This measurement includes the loading of the transformer / 10R to the generators output and differs from the transformers response. For an advanced measurement, apply the same generator to the input, keep the 10R termination and measure both voltages (input and output) at the same time, then calculate their ratio - this gives the transformers response alone. I'm not familiar with the Analog Discoveries possibilities, it should offer some kind of Bode Plot feature with two input voltages and one generator output, this is what you want.

author: precaud
author_rank: Frequent Contributor
timestamp: August 02, 2018, 01:53:09 pm
content: Quote from: capt bullshot on August 02, 2018, 01:31:13 pmWhy the 10R? Does that reflect how you most often use them?

author: capt bullshot
author_rank: Super Contributor
timestamp: August 02, 2018, 02:12:59 pm
content: Quote from: precaud on August 02, 2018, 01:53:09 pm10R is the value the Omicron transformer is specified for (recommended 1R ,,, 10R afair). Just to be comparable - e.g. I did the measurements for my home rolled transformer with 50R termination and get different results.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 02, 2018, 02:20:03 pm
content: Yes, skin effect dominates by ~20kHz or so, at which point the core resembles a Warburg element.Example:Approximate equivalent circuit:An upside to this for EMC purposes: the Q is very low as the impedance rises towards peak, so that you can pair the CMC with a modest capacitance and not worry about resonance. Because the mu, going into this region, starts higher than it is for ferrite, and hi-mu ferrite drops off (~single pole) at a roughly similar frequency (usually ~100kHz, but depends on core size), nanocrystalline has a wider and taller impedance peak than ferrite does, making it just that bit better.Tim

author: Bud
author_rank: Super Contributor
timestamp: August 02, 2018, 02:36:03 pm
content: QuoteQuoteLow value load impedance Because of the way injection transformers are used. To inject the signal into the power supply control loop you break the control loop connection and insert a low value resistor in it in series across which you then connect the injection transformer. Resistor values up to 10 Ohm seem to be reasonable to not have effect or have minimal effect on the control loop under test. 50 Ohm may be too high, i'd shoot for and test with 10 Ohm.

author: precaud
author_rank: Frequent Contributor
timestamp: August 02, 2018, 02:54:25 pm
content: Quote from: Bud on August 02, 2018, 02:36:03 pmOK, got it. I've not done it myself, but most of the R's I've seen used for control loop repose were higher than 10R, more like 33-50.

author: Hydron
author_rank: Super Contributor
timestamp: August 02, 2018, 03:06:47 pm
content: 50R seems reasonable unless the feedback divider values are unusually low. When I've done this type of testing (using a video isolation transformer, as I did not have my isolated sig-gen available) 50R worked well. The actual value will not be critical as long as it's reasonable.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 02, 2018, 03:27:28 pm
content: Another reason to use a very low termination resistor for an injection transformer is bandwidth. The lower the termination resistor, the higher the bandwidth.Another trick to increase bandwidth in an injection transformer is a (lossy) matching network at the primary side. This damps out resonances and flattens frequency response.Enhanced by these tricks, even very normal off-the-shelf signal transformers can be successfully used up to a few 100kHz.The loss is normally no problem because the injected signal needs to have a very low amplitude.https://electronicprojectsforfun.wordpress.com/injection-transformers/shows some of these.

author: precaud
author_rank: Frequent Contributor
timestamp: August 02, 2018, 03:33:37 pm
content: Quote from: Wolfgang on August 02, 2018, 03:27:28 pmHmmm... I see exactly the opposite. I'll post some results later.

author: DualTriode
author_rank: Contributor
timestamp: August 02, 2018, 06:34:49 pm
content: Hello,For grins this is a plot of the Jensen ISO-MAX VB-1BB 75 Ohm isolation transformer on ebay for $20. Not bad for $20, if price is the object.The second plot is the Home-Roll. Can't tell it from the B-WIT.Both plots 401 test points from 1Hz to 25MHzThanks DT

author: rx8pilot
author_rank: Super Contributor
timestamp: August 02, 2018, 07:16:57 pm
content: I have the same Jensen ISO-MAX.... seems like a great bang for your buck.Short and misplld from my mobile......

author: precaud
author_rank: Frequent Contributor
timestamp: August 03, 2018, 03:12:42 am
content: Quote from: Wolfgang on August 02, 2018, 03:27:28 pmHere's the NH 0016PA transformer with 50 Ohm source and 1 terminated with 50, 10, and 1 Ohm. Bandwidth goes from >20MHz @ 50 Ohms to ~150kHz @ 1 Ohm. This is pretty typical of the better 1:1 xfmrs I've looked at. You can get a little of the bandwidth back with lower source R.

author: DualTriode
author_rank: Contributor
timestamp: August 03, 2018, 05:07:58 am
content: Hello,All this talk of termination resistors.Is this with a resistor intentionally placed across the secondary winding plus the resistance to ground internal to the VNA?That means that we have the external resistor across the secondary coil in parallel with the instrument internal resistor to ground.Different related topic.It is not so much about adding additional resistance to extend or reduce bandwidth it is about resistance being used to tune or critically dampen the native inductance of the coil. Another way to think of it goes like this. Inductance is often added to RF circuit to increase Q and extend bandwidth with inductive peaking.Thanks DT

author: JS
author_rank: Frequent Contributor
timestamp: August 03, 2018, 08:48:37 am
content: Quote from: DualTriode on August 03, 2018, 05:07:58 amThe resistor is added because you want low resistance to use the transformer, so you want to know the response of the transformer in its intended way. You want such resistance to reduce the impact of the insertion of the transformer onto the DUT.JS

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 09:09:11 am
content: What about also *driving* the transformer from a very low impedance !Its the old rule of thumb: The lower 3dB corner sits where inductive impedance is ca. 4 times the feeding and terminating impedances.So, when the feeding impedance is just a few ohms and the inductance stays the same, the low frequency corner is improved.

author: precaud
author_rank: Frequent Contributor
timestamp: August 03, 2018, 12:53:21 pm
content: Quote from: DualTriode on August 03, 2018, 05:07:58 amYes. But the VNA Rterm is usually set to 1MegOhm for these measurements.QuoteYes, but its not always actually present in use. It depends on what you're using the transformer for, and what the load presented to it is..QuoteThat works really well if the circuit on the secondary side is fixed, and you can tailor it to the xfmr. I used to do that when designing transformer-coupled mic preamps, optimizing the xfmr RC termination for flattest input impedance and/or freq response. (Deane Jensen was a mentor of mine, and showed us all how to do this back in the 80's.)But this RC compensation doesn't work when the circuit on the secondary side is an unknown load which you're injecting a signal into. That load is in parallel to whatever Rterm (if any) is across the 2ndary. In that case we want no termination resistor, but we need to deliberately terminate the xfmr with a range of loads it will encounter to see how its characteristics change.Here's an example, a circuit HP used to recommend for their VNA's to measure output impedance of DC voltage regulators. This is an easy circuit to use with VNAs because of the 1 Ohm current multiplier. Using short and load compensation, I get good results with it down to 10mOhm or better.The transformer they recommended was the North Hills 0017CC, shown earlier in this thread, a 50 Ohm 1:1 unit rated at 5MHz BW (7.5MHz actual). In this circuit the xfmr is operating at load impedance of (1 Ohm + Zdut) at each freq. At those loads the xfmr bandwidth is varying dramatically with load Z. The useable bandwidth of the 0017CC at 1 Ohm is less than 100kHz (more like 10kHz if you want to measure phase accurately, see the plots a couple posts up for the similar 0016PA). And that's why HP's Z plots for this technique only go to 100kHz, even with the 500MHz analyzer. The xfmr bandwidth into 1 Ohm is the limiting factor.Hope this helps.

author: precaud
author_rank: Frequent Contributor
timestamp: August 03, 2018, 12:56:13 pm
content: Quote from: Wolfgang on August 03, 2018, 09:09:11 amYes, it extends the bandwidth some, but my VNAs all have 50 Ohm outputs, so an external amplifier with direct-coupled output is required to do it.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 01:21:33 pm
content: I did it the primitive way and I added a voltage divider with 50 Ohms impedance for the generator and only a few Ohms to drive the transformer.Loss is welcome because levels should be very low and it also dampens out resonances.See here:https://electronicprojectsforfun.wordpress.com/injection-transformers/

author: precaud
author_rank: Frequent Contributor
timestamp: August 03, 2018, 01:41:39 pm
content: Quote from: Wolfgang on August 03, 2018, 01:21:33 pmFor control loop response, that works, since you need only small injection signal. How high are you trying to measure? Most ones I've seen only look at 100kHz and below.QuoteYes, I've seen that, it is relevant for control-loop-response but not for using a xfmr for output isolation (breaking ground loops for low-level measurements, aka "braid error").

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 01:52:53 pm
content: Hi,my measurement go up to a few 100kHz only. They are mostly for linear power supply for measurement circuits where low noise is an issue (like preamps for noise measurements, ...). Funny enough, even battery powered supplies have noise peaks.For the "braid error" issue I am working on another approach injecting current and measuring voltage response of a PSU. In these cases I do not need a transformer,but an active injector, the same ideas like the PicoTest ones. Stability can then be inferred by extracting data from the Nyquist plot of the output impedance.This is work in progress, but in September I can get my hands on a Keysight E5061B-3L5 (VNA from 5Hz to 3GHz), and then I can properly measure all my homebrew stuff without improvisation.There are nice appnotes from Keysight how a VNA can be used to measure milliohm impedances in PDN networks. I learned a lot from those.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 03, 2018, 01:58:00 pm
content: Quote from: precaud on August 03, 2018, 12:56:13 pmIf there is no need for high power, one could use a simple shunt resistor at the input side of the transformer. Even with a 50 Ohms output it lowers the impedance, but also the amplitude. If needed (e.g. longer cables) one could add series resistance to get back 50 Ohms impedance for matching.For the normal use, one would also measure the transfer characteristics of the transformer. So the measurements could be done beyond the 3 dB point. With a not so large load resistance an the secondary side the extra loading by the circuit should not have that much effect. With correction it's no so much die transfer function that matters, but how stable this function is.Besides the forward transfer function, one might have to care about the coupling capacitance. If the point where the injection transformer is used is high impedance, this is likely the more important limitation. So in a power supply the transformer should go right between the output and the divider - the point between the divider and the FB amplifier would be more like bad choice, as it is high impedance and a few 100 pF can really make a difference.

author: precaud
author_rank: Frequent Contributor
timestamp: August 03, 2018, 02:12:25 pm
content: Quote from: Wolfgang on August 03, 2018, 01:52:53 pmMost of these xfmrs will work for you, then.QuoteI look forward to seeing your results!QuoteAgreed. The "shunt-thru" technique can give good results into higher freqs.

author: DualTriode
author_rank: Contributor
timestamp: August 03, 2018, 05:22:27 pm
content: Hello,Now that the conversation regarding the termination resistor is near complete take a look at page 8 figure 4.1 of the Omicron Lab injection transformer manual. The recommended injection resistor value is between 1R and 10R.https://www.omicron-lab.com/fileadmin/assets/Bode_100/Accessories/B-WIT_100/B-WIT-B-LFT-User-Manual-V1.1.pdfNow looking at injection transformer phase measurements:The transformer phase plot shows the phase difference between the transformer primary and secondary. Some folks here say that the injection transformer is no longer useful when phase exceeds some value plucked from the chart. This needs a closer look.If you look at the Signature Bode 100 gain vs Phase Margin chart, the point where gain is equal to 0dB the PM gives a very good indication of power supply stability. Doesn’t the injection transformer phase effect the PM of the power supply? The short answer is no.Thanks DT

author: precaud
author_rank: Frequent Contributor
timestamp: August 03, 2018, 08:55:55 pm
content: Quote from: DualTriode on August 03, 2018, 05:22:27 pmMore precisely, it can be used with R's from 1R to 10R, with 10R recommended.QuoteWell of course not. That isn't the question. The question has to do with the accuracy of the measurement.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 04, 2018, 11:53:18 am
content: If you want infinite bandwidth from such a transformer, and don't mind a flat 6dB insertion loss: split the transmission line in the middle, and add terminations here. You need an R+C across the (now open) ends of these windings, where:R = ZoC >= 2.5 * k * (377Ω) * t_half / Zo^2k = effective dielectric constant (note this is less than the material k itself, when the dielectric is mixed, e.g., microstrip, twisted pair, foam, etc.)t_half = transmission line electrical length (units of time)This terminates the half-windings, so the transformer looks like a pair of Zo resistors from P1 to S1 and from P2 to S2. Obviously, this breaks transformer action.One might rightfully note this isn't a transformer at all anymore, and the circuit can be greatly simplified by removing the transformer altogether; now you have coupling capacitors (the termination resistors are completely optional, unless you liked the insertion loss), and the CMRR is still just as bad, although it's bad at low frequencies too (oh well?).To restore transformer action, connect across the cut ends (primary middle to primary middle, secondary middle to secondary middle) with inductors, of similar value (i.e., L ~ Zo * t_half). Now you get asymptotically zero insertion loss at low frequencies, and at high frequencies, a 6dB shelf instead of the dips and peaks.Aside of all of this, CMRR is asymptotically bad in the HF limit. To address this, place a CMC on either side of the transformer, as much (equivalent) inductance as you can afford. Add damping R+C across the transformer (P1 to S1, and P2 to S2) to control resonances, if necessary (these will be a large impedance, so will have little impact on HF response, despite their location). The CMC inductance will resonate with the transformer isolation capacitance (and coupling/termination capacitance C, if used, as above), so this prevents that resonance from getting too peaky. An isolation impedance in the low kOhms is very reasonable to achieve this way, and while that doesn't sound terrifically good, understand that we're talking with respect to radio frequencies here, where a thin wire in semi-free space is unlikely to reach half a kohm Zo. This is doing as well as you can, given the limitations of real electromagnetism and not just some inductors and capacitors in a SPICE model.Tim

author: Wolfgang
author_rank: Super Contributor
timestamp: August 04, 2018, 02:37:45 pm
content: Quote from: DualTriode on August 03, 2018, 05:22:27 pmWhat you write reminds me of a hefty discussion following a Texas Instrument Application note where they used a garden variety line transformer as an injection transformer and claimed its characteristics are irrelevant because it was "outside the loop".It is OK to claim that (provided the secondary resistance is small enough) it does not alter the characteristics of the loop, but what it does alter is the amplitude and phase you measure at the loop output. You could calibrate this out using a VNA, but it is definitely a precision issue. When you look at the characteristics of the magnetic materials used for such transformers, the range of mu for a given frequency is 2 to 1. You can expect an coresponding low precision range for band corners. If your measurements are to be trusted, the phase shift induced by your transformer must be a) small and b) well known.

author: precaud
author_rank: Frequent Contributor
timestamp: August 04, 2018, 04:27:57 pm
content: Here's a plot I made last year of the 10Hz - 10MHz magnitude response including some of the transformers mentioned in this thread, with 50 Ohm generator output, and xfmr terminated with 1 Ohm.Curves from top down:The dark blue is a toroid Tokin 10mH CM choke.Magenta is the Jensen Iso-Max mentioned here several times. It is coax wound on a standard EI core, no doubt with carefully-chosen core material...Green is the North Hills 0016 PAYellow is the North Hills 0017 CCRed is a North Hills 1307 LB 75 Ohm unbal to 110 balanced transformer, used as a makeshift step-down xfmr, with one side of the 2ndary terminated in 50 Ohms and the output taken from the other side. Even this mild stepdown is sufficient to extend phase linearty vs Z to just beyond 100kHz, and so this is the xfmr I use with the circuit shown in post #102.Cyan is a Ridley 15MHz Injection Transformer, a 10:1 step-down design, IIRC.I would expect that the B-WIT 100 and the home-rolled version would behave pretty much the same, rolling off somewhere around 100kHz.It would be interesting to make a 2:1 or 3:1 version to extend the 1 Ohm bandwidth. Hmmm...EDIT : I learned yesterday that the Ridley is a 3:1 step-down winding ratio.This makes it even more compelling to do a home-roll 2:1 or 3:1 version...

author: capt bullshot
author_rank: Super Contributor
timestamp: August 06, 2018, 11:42:11 am
content: Hey guys and girls, I've just found out the secret sauce that North Hills adds to their wide bandwidth transformers.....Yes, its "Bauschaum" (polyurethane foam)This is a NH 12369 (obviously) video isolation transformer. Anyone's got a datasheet? I didn't find one. Will do some measurements later.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 06, 2018, 11:51:00 am
content: Interesting that there's silver mica caps in there.Pot cores are quite good, having more A_L than a toroid of the same size -- which means less wire length and more transformer bandwidth. (Too bad amorphous isn't available in shapes!)Tim

author: capt bullshot
author_rank: Super Contributor
timestamp: August 06, 2018, 04:23:30 pm
content: transformer pr0nThe unit has 4 channels, three of them intended for video and one sync.The sync channel has a small cap (labelled "100") across the input BNC.The video channels have the silver mica ("471") connected from input (presumably BNC shell) to output (BNC shell).The transformers are wound using twisted enamelled wire, the video channels have thicker wire than the sync channel.

author: capt bullshot
author_rank: Super Contributor
timestamp: August 06, 2018, 04:29:16 pm
content: Some results:The video channel has a magnetizing inductance of 112mH and the input to output coupling capacitance is 1.13nF (measured quite similar on all three channels).For the sync channel, the results were 977mH and 1.9nF.The frequency response (-3dB) for the video channels is 50Hz ... 78MHz, but the 45° phase shift response is from 50Hz to 14MHz - some tricks happening here - Note the bumps in the frequency response above 1MHz. This response looks the same for all three video channels. Termination was 50 Ohm for all measurements.The sync channel shows a clean response from the low end of the HP3577A (5Hz) to 7.5MHz.Estimating the wire length with the TDR shows a pretty clean impedance over length, somewhat varying around the expected 75 Ohm. Maybe 1.8m for the video transformers and around 6.8m for the sync. Assuming the real length in this ballpark, the high frequency response is way much better than the home rolled transformer using the nanocrystalline / amorphous core.Pretty good stuff this is!

author: precaud
author_rank: Frequent Contributor
timestamp: August 07, 2018, 01:40:24 pm
content: Quote from: capt bullshot on August 06, 2018, 04:29:16 pmI'm guessing you're using the 50 Ohms term in the 3577A. If you terminate the xfmr right at its output and set the analyzer to 1MegOhms, the mag/phase correlation at the high end should make more sense.QuoteAgreed!

author: capt bullshot
author_rank: Super Contributor
timestamp: August 08, 2018, 04:06:52 pm
content: Quote from: precaud on August 07, 2018, 01:40:24 pmYes, I'm using the internal termination. Shifting the termination towards the transformers output and setting the input to 1M doesn't make it any better, in contrary one can see even more bumps in the frequency response. I've used a rather short coax cable to connect the terminated transformer output to the 3577A. Maybe one would get better or at least other results using a compensated 10:1 oscilloscope probe.In general, I'd prefer to see the transformers response when fed and terminated by its nominal impedance (75 Ohm for video stuff). I don't have the minimum loss pads to match to 3577A's 50 Ohm ports, so for now I'll stay with the 50 Ohm measurements.And for the records, I'm making the measurement from Output to R input, in contrary to using a power divider and A/R as I prefer to see the system response over the transformers response fed from a virtual zero ohm source. Using the power divider and A/R measurement gives different results with notably extended low frequency response.

author: DualTriode
author_rank: Contributor
timestamp: August 08, 2018, 05:03:56 pm
content: Quote from: Wolfgang on August 04, 2018, 02:37:45 pmHello,I don’t know anything about a garden variety (straw man) line transformer.I do agree there may be a falloff in amplitude. Both the Keysight and Bode 100 have built in provisions to adjust the test amplitude to within the small signal requirements of the error amplifier control loop. Even the best specialized injection transformers may sometimes need a little help.I have seen no evidence that the change in phase in the injection transformer is evident in the phase measurement between the input of the error amplifier loop and the power supply output.Any transformer, even the best specialized injection transformers may get a little wobbly if pushed into the anti-resonance/ resonance frequencies.Thanks DT

author: precaud
author_rank: Frequent Contributor
timestamp: August 08, 2018, 05:06:25 pm
content: Quote from: capt bullshot on August 08, 2018, 04:06:52 pmWhen it comes to xfmr-coupling, I'm a fan of "whatever works"QuoteI'm not using a power divider, either. What is your "virtual zero ohm" source ?QuoteTo me, characterizing a xfmr is set up like an FRA measurement; A/R, source Z same as it will be used, no power divider, high-Z inputs, and xfmr terminated in whatever the desired load is.

author: rx8pilot
author_rank: Super Contributor
timestamp: August 08, 2018, 05:18:16 pm
content: Quote from: precaud on August 08, 2018, 05:06:25 pmHow do you calibrate/normalize this setup?

author: capt bullshot
author_rank: Super Contributor
timestamp: August 08, 2018, 06:06:27 pm
content: Quote from: precaud on August 08, 2018, 05:06:25 pmThat's was mistake in my conceptual thinking, whatever. I assumed, measuring the signal output at one side of the power divider would compensate for the total loading effect on the source. But it doesn't, it attenuates the loading effect to a lower impedance seen by the VNA - assuming using a resistive power divider. Anyway, measuring both the transformer input and output with high impedance R and A, then calculating A/R removes the loading effect of the transformer from the result. That's nearer to a virtual zero source impedance than the power divider method.In practical appliation, e.g. for the said video stuff, one cannot take the loading effect out of the system, so I normalize R (transformer replaced by a "through") and then put the transformer in place to see the system response.rx8pilot:You'd normalize the "FRA" setup by setting the VNA to sweep A/R phase and amplitude, the replace the transformer by a "through" and normalize. The 3577A then normalizes these traces (resulting in "A/R/D1" / "A/R/D2" as traces). This is at least how I'd normalize this setup. precaud pls confirm.precaud:At above some 10MHz the high impedance input mode of the 3577A doesn't work too well anymore, because of the 50 Ohm impedance of the internal and external cables involved. For lower frequencies, high Z should work fine and wouldn't require normalization anyway.

author: capt bullshot
author_rank: Super Contributor
timestamp: August 08, 2018, 07:29:49 pm
content: Couldn't leave that stuff alone ...So I bodged a pair of minimum loss pads (50 Ohm <-> 75 Ohm) together and measured the video transformer again:-3dB from 60Hz to 100MHz, +/-45° phase at 60Hz / 13Mhz, similar to my 50 Ohm measurement with the low frequency response shifted up (as one would expect from the increased source / sink impedance). Still some smallish bumps in the amplitude response above 1MHz.Now, after some thinking, I replaced the "through" calibration piece (a male-to-male BNC adaptor) with a piece of 75Ohm coaxial cable of similar length to the guessed wire length within the transformer - somewhere in the 1.8m range.After normalizing to this "through reference", the result is (guess what):same as above for -3dB, but -45° phase at 45MHz.So the internal wire length of the transformer causes some delay that leads to the misinterpretation -3dB implausible to phase.BTW:TDR'ing the transformer through the minimum loss pads shows a quite flat line - so these transformers clearly are made for 75 Ohm system impedance and have an impressive bandwidth then.BTW 2:The 3577A's "Length" setting achieves the same result as normalizing with the "through cable". Just set it to the negative value of your additionally introduced cable length to compensate for this.BTW 3:Pushing Leo Bodnar's fast pulses through the transformer gives a risetime of 4ns (vs. 400ps w/o the transformer, measuring the scope and matching pads). The transformer also adds some ringing to the square wave.

author: precaud
author_rank: Frequent Contributor
timestamp: August 09, 2018, 12:55:43 am
content: Quote from: capt bullshot on August 08, 2018, 06:06:27 pmWell there can be good reasons for looking at it either way. I'm just concerned that future readers of this thread will look at all the measurements as if they're the same, when they're not.QuoteYes, and make sure whatever you'll be loading the xfmr with is in place for the sweep you use for normalizing.QuoteYes, for true high-Z measurements that wold be true. But not so much for a device with a 50 to 75 Ohm term. You can use normalize to test the impedance sensitivity of the measurement setup. Ex: normalize a "thru" sweep with 50 Ohm term, then change to a 75 Ohm term and it will plot the deviation. Anything that is not a flat line is a problem... phase deviation would be the most sensitive.That's phenomenal bandwidth you're getting through that xfmr! What is it rated for?

author: rx8pilot
author_rank: Super Contributor
timestamp: August 09, 2018, 01:10:49 am
content: This thread has thrown me down a rabbit hole of thoughts, self-education, and experiments. Only learning more about magnetics and properly measuring them with a 25-year-old VNA can get me out of the hole.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2018, 03:05:12 am
content: Quote from: rx8pilot on August 09, 2018, 01:10:49 amIf it gets more people measuring, it can't be a bad thing.Tim

author: capt bullshot
author_rank: Super Contributor
timestamp: August 09, 2018, 05:16:32 am
content: Quote from: precaud on August 09, 2018, 12:55:43 amDon't know. Found it by chance on the evilbay (looking for North Hills after someone mentioned their transformers here), and decided to give it a try. No datasheet, no information, no similar part number found on the North Hills website. BTW, they've got some app notes about transformers and other interesting stuff.So I just could guess: It's a RGB + sync video transformer, so I expected it to have wide BW to be useful, or it would be a common mode choke (North Hills calls them "Humbucker"). Former analog monitors having BNC RGB inputs achieved video bandwiths in excess of 100MHz.http://www.nhsignal.com/products-wideband-video-isolation.html

author: ehughes
author_rank: Frequent Contributor
timestamp: August 09, 2018, 09:01:11 pm
content: For what its worth, Omicron got at least 1 sale as a result of the tear down. I just ordered one for QA checking out transducers. Once it is up an running, I'll post some measurement results.

author: precaud
author_rank: Frequent Contributor
timestamp: August 11, 2018, 06:01:04 pm
content: I see now where the 10 Ohms term comes from. Omicron uses is as the reference R for their low-Z measurements using the transformer:https://www.omicron-lab.com/applications/detail/news/low-value-impedance-measurements/I'm surprised they're not getting a higher useful bandwidth using the 10 Ohm reference (which also determines the minimum load on the transformer). I get 100kHz using similar topologies using a 1 Ohm reference.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2018, 06:12:29 pm
content: Bandwidth is maximum at Zo, and drops off slowly for Z <> Zo. The first-order approximation is thus: if LL and Lp are constant, then the LF cutoff is Z / (2*pi*Lp) and the HF cutoff is Z / (2*pi*LL).For the frequencies and materials we're talking about here, this should be pretty close. Note that the HF cutoff is actually a transmission line effect, not a dominant pole, so it will have slightly different response into other resistances (I forget if this is better or worse for BW). For worse quality materials (like laminated iron), the permeability dependence on signal level and frequency is probably an important factor.Tim

author: precaud
author_rank: Frequent Contributor
timestamp: August 12, 2018, 03:25:57 pm
content: This is a pretty interesting video, Ray Ridley comparing the three commercially-available isolation xfmrs at low frequencies.Unit "P" is clearly the Picotest.Unit "O" is the Omicron.I do wish he had also plotted transmission curves vs freq over the whole range of the transformers, measured into the same load R.I had the Ridley 15MHz unit and it had a 10dB dip starting at around 10kHz, regardless of load.

author: chris_leyson
author_rank: Super Contributor
timestamp: August 12, 2018, 04:16:17 pm
content: The Omicron Labs B-WIT 100 is only supposed to be driven at 0dBm not 13dBm. Interesting video from Omicron Labs where product "R" gets tested.

author: precaud
author_rank: Frequent Contributor
timestamp: August 12, 2018, 04:38:24 pm
content: Yeah, the 15MHz Ridley unit I had looked similar in terms of flatness, though smoother at the high end than that one. The freq resp dip bugged me and so I sold it (perhaps hastily).However, one could argue that, as long as the response does not change with level or load, and the variations are not extreme, for most FRA work, ultimate flatness is not critical...

author: Wolfgang
author_rank: Super Contributor
timestamp: August 12, 2018, 05:29:48 pm
content: Unfortunately, neither Ridley nor Omicron tried to be especially objective with their presentations.What would have been helpful are S21 curves that go over the whole frequency range, at given load impedances (e.g. 1/5/10/20/50 Ohms),plus a curve for the allowable signal level for, say, 1% distortion over frequency, also for different load impedances. Also phase response is importantto know about.It is very clear than one single device hardly fits all needs (High bandwidth, tolerant to strong signals with no distortion, low capacitances, not bulky ...)There will versions with a deep low frequency limit - they are heavy and bulky, have a high coupling capacitanceThere are smaller ones, which are small signal only, have medium frequency ranges, but lower capacitances, ......and the HF ones with very high bandwidth, very small signal tolerance, and small capacitance.All marketing claims made in this industry has to be taken with a huge ROCK of salt. So have these videos.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 12, 2018, 07:36:16 pm
content: If a really good injection transformer is that difficult, I would consider thinking about an active solution, with optical isolation, thus a kind of analog opto-coupler. In a simple form something like 2 photo-diodes in parallel to a load resistor. Without amplification it would be likely limited to low power (e.g. a few 10 mV) - but chances are it could work from DC to beyond 10 MHz with low coupling capacitance. If it needs an amplifier for the output this could be battery powered for good isolation.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 12, 2018, 07:44:54 pm
content: Yes, this is a valid approach. If it is battery-powered and has a very fast (also low noise) optical isolator it competes very well with transformer solutions, especially at the low frequency range.

author: ehughes
author_rank: Frequent Contributor
timestamp: August 16, 2018, 06:12:08 pm
content: We just got our Bode100. It is a very nice piece of equipment and the software that come along is useful. We are doing some analysis of a 1.8MHz piezo ring. Specifically, we are able to evaluate the epoxy in a transducer assembly.Yet nice piece of equipment and easily worth the money for our QA setup.

author: voltsandjolts
author_rank: Unknown
timestamp: August 18, 2018, 08:11:55 pm
content: I was browsing the Picoscope site (I'm interested in their flexres 16bit/8bit scopes with arb gen that can do FRA) and found quite a nice video link about measuring loop gain with a DIY signal injection transformer. Looks like a nanocrystaline core from a common mode choke with about 7 metres of TP each for primary/sec - its at 9:00 minutes in, but the whole video is quite well done. Didn't achieve the bandwidth that others have here thohttps://youtu.be/wKs8VyERZXU

author: precaud
author_rank: Frequent Contributor
timestamp: August 20, 2018, 04:32:32 am
content: Here's a good reason NOT to use the Jensen IsoMax transformer for gain- and phase- margin measurements above 20kHz - above which the phase response changes with impedance... caused by the bandwidth increasing with increasing load R. The North Hills units are all better in this range.

author: DualTriode
author_rank: Contributor
timestamp: August 20, 2018, 09:34:55 pm
content: Hello,What you have shown is that the leakage inductance and load resistance form a low pass filter.What you have not shown is that accuracy of the VNA Bode Plot is diminished.The Bode Plot Phase Margin is independent of the transformer phase.(within limits) The VNA software has provisions to compensate for the attenuated transformer HF gain. (within limits)DT

author: precaud
author_rank: Frequent Contributor
timestamp: August 20, 2018, 11:01:26 pm
content: Quote from: DualTriode on August 20, 2018, 09:34:55 pmI haven't "shown" it, but I guarantee you it definitely is diminished, unless some post-processing is used to correct for it (Open/Short/Load). But even then, if the change is not fairly linear over the entire measurement range, the compensation math won't b able to correct for it accurately.QuoteNot in my experience.QuoteYes, some VNAs have "provisions" for it, but I have never seen any example of someone "normalizing" their VNA with the transformer in place prior to making a control loop measurement.

author: rx8pilot
author_rank: Super Contributor
timestamp: August 20, 2018, 11:12:06 pm
content: Curious why you started at 4R7.What are you using to test it? How did you calibrate? I may do the same test to see if the results are similar (although I may use higher value loads) - but would want to match what you did.

author: precaud
author_rank: Frequent Contributor
timestamp: August 20, 2018, 11:36:54 pm
content: Quote from: rx8pilot on August 20, 2018, 11:12:06 pmI didn't; I started at 1R0, and ended at 4R7Most of what I use these for (output impedance measurements) loads the transformer between 1R0 and 5R0 on the high end. See the setup in this post:https://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/msg1720265/#msg1720265For the measurement I posted, the setup is the same xfer function setup as others I've posted; both inputs at 1M, R measures xfmr input, T measures the output.QuoteAP Instruments 102BQuoteHuh? You want me to explain the 102B's cal procedure?QuotePlease do. I get the same results regardless of the analyzer used.

author: chris_leyson
author_rank: Super Contributor
timestamp: August 20, 2018, 11:50:00 pm
content: @voltsandjolts Nice video from Picoscope, thanks. Something has been bugging me about using 1:1 transformers and them terminating the secondary with 5 or 10 ohms. I would have gone for 2:1 or most probably 3:1 for a 5 ohm load. If I get time this week I will have a stab at a 3:1 transformer and see how it goes.

author: DualTriode
author_rank: Contributor
timestamp: August 21, 2018, 05:21:29 am
content: Hello,Open/Short/Load calibration is used for the impedance accessory test fixture and is not part of the VNA frequency gain / phase plot.If you look in the Keysight E5061B User’s Manual you will the Open/Short/Load calibration procedure for Impedance Analysis option and optional impedance test fixture(s).The available adjustment for the Frequency Gain / Phase Margin test is signal level. There is no adjustment needed for transformer phase.The available test signal adjustment is for amplitude. The generator output level is adjusted to be within the small signal range of the DUT error amplifier. Over the LF range the signal level may need to be trimmed to reduce noise. Over other frequency bands the signal may need other tweaking. This tweaking is a iterate process looking for the cleanest Bode plot. This tweaking is more about the DUT than the injection transformer. (within limits)DT

author: Wolfgang
author_rank: Super Contributor
timestamp: August 21, 2018, 11:05:31 am
content: I agree completely.The properties of your isolation transformers determine your dynamic range, even if the phase and amplitude response can be calibrated out by a good VNA.What I do not understand in a lot of cases why manufacturers insist so much on a 1:1 ratio. I do not know a lot of examples except PFC where high signal injection amplitudes at low frequencies are really needed; In the absolute majority of cases you need rather small amplitudes in the millivolts range in order not to drive the DUT out of its linear range.I did it with COTS ISDN transformers and a matching network., and it worked fine.

author: precaud
author_rank: Frequent Contributor
timestamp: August 21, 2018, 12:42:28 pm
content: Quote from: DualTriode on August 21, 2018, 05:21:29 amMy point exactly. So what exactly are you referring to when you said "The Bode Plot Phase Margin is independent of the transformer phase.(within limits)" ?QuoteYes, its unfortunate E5061B users need to buy an optional fixture to do it. We're not limiting our discussion to any particular analyzer. What one are you using?QuoteAnd that's where we disagree. If you make a measurement in a freq range where the xfmr magnitude and/or phase is not linear, it transfers directly into your measurement. How could it be otherwise? If would try it, you would see it is so.QuoteYes, that is for control loop testing. For impedance testing, the amplitude considerations are different. But it's not either/or; the same transformer can be used for both measurements, as long as you characterize it at the load it will be seeing, and use it within that range.No matter what, the transfer response of the xfmr at the load it will see needs to be paid attention to.Quote from: chris_leyson on August 20, 2018, 11:50:00 pmFor impedance testing, I agree, and look forward to what you come up with. I'm gathering bits together to do a 2:1. For control loop, a 1:1 into 10 Ohms or above should be sufficient.Quote from: Wolfgang on August 21, 2018, 11:05:31 amBecause they're easy to make. And they generally do the job.

author: capt bullshot
author_rank: Super Contributor
timestamp: August 21, 2018, 01:22:13 pm
content: Quote from: precaud on August 21, 2018, 12:42:28 pmSo if you look up the AP Instruments Model 102B Manual (I found one here:http://www.apinstruments.com/files/102Bman.pdf), Page 54 (PDF numbering) / 50 (document numbering) shows your typical FRA setup used. The VNA calculates the frequency response from the ratio of its inputs Channel A and Channel B. So the Source impedance and transformer phase / amplitude cancels out from the equation. No calibration required, just a good matching between Channel A and B (which one expects from a decent VNA).Within limits of course, since one needs a minimum amplitude of source signal coupled through the transformer to get a useful signal above the noise floor.Quote from: precaud on August 21, 2018, 12:42:28 pmSame reason as above, the measurement of Channel A / B ratio cancels the transformer out of the equations.

author: precaud
author_rank: Frequent Contributor
timestamp: August 21, 2018, 01:35:52 pm
content: Quote from: capt bullshot on August 21, 2018, 01:22:13 pmOK, I see, for that topology the xfmr is literally doing nothing more than "injecting" the signal. So the xfmr requirements are relaxed, compared to what they are when using it for impedance measurement.

author: rx8pilot
author_rank: Super Contributor
timestamp: August 21, 2018, 06:16:57 pm
content: Quote from: precaud on August 20, 2018, 11:36:54 pmI know the question sounds fundamental - and it is. This is a topic that I am new to and I have very little confidence in the results I am getting. I have been trying to better understand the network analyzer (in a general sense, not model specific), inductor measurements and analysis, and frequency response analysis of SMPS control loops. One of the things I am trying to figure out is essentially a 'sanity check' to make sure the results I am getting are reasonably accurate.The part that I worry about is getting results that are close - but skewed enough that I end up chasing my tail. I don't have a solid intuition of how sensitive the measurements can be, where I can get false/skewed measurements and such. I think back to when I was learning to use an oscilloscope to measure delicate signals and the 10x passive probe had a huge ground clip connected directly to the power supply terminal. Everything looked broken, of course, and I spent a long time trying to add capacitors to reduce phantom noise. At some point - I learned how to use the instrument properly and of course, realized that there was never a problem - the measurements themselves were the problem.Perhaps gathering the manuals for the AP VNA, Bode100, E5061-LF, etc would help me gain some confidence in how I am going about the process. Repeating some of the measurements in this thread should also help since I have the Jensen ISO-MAX VB-1BB that has been measured by a couple of people (comparison)

author: capt bullshot
author_rank: Super Contributor
timestamp: August 21, 2018, 06:53:33 pm
content: rx8pilot:For building up some confidence in the cal and measurements procedures, I'd recommend to rebuild the HP35676A test set:http://hparchive.com/Manuals/HP-35676-SCHEMATIC.pdfNo need for all the fancy metalwork, and don't worry about the unknown capacitor, it still works built on a piece of SMT protoboard using some MiniMelf resistors (some of the series connected to get near the original value).Once calibrated using the full cal procedure (again, no need for a fancy cal standards set, a wire and a 50 Ohm resistor works, you'll get some ripple at the 200MHz end), then switching the 3577A to impedance display (choose "F4" as the input to display , it's written somewhere in the manual), you can get impedance sweeps of known components (start with resistors in the 10 Ohm to k Ohm range) and get familiar with the way it works. Measure some inductors and capacitors, read the imaginary part at some frequencies and do the math to verify your reading. Inductors are quite fancy regarding their impedance over frequency, many of them are inductors at rather low frequencies only.There's also somewhere a manual on the net (for this or the HP35677 test set) that has a better description of how to measure impedance using the 3577A than the 3577A manual.Edit: Found it, here it is:https://cb.wunderkis.de/wk-pub/Keysight%2035676A%20Data%20Sheet.pdfEdit 2: Don't know what you mean by "skewed", the manual has some tips regarding the RBW setting: Reverse the sweep direction and watch if the graph shifts. If it does, your sweep speed is to fast for the chosen RBW.Edit 3: "F4" is impedance for a 50 Ohm system and calibration, "F5" is for 75 Ohm

author: DualTriode
author_rank: Contributor
timestamp: August 21, 2018, 07:11:14 pm
content: Hello,This is looking for the Sweet Spot.Most of these injection transformers are set up for only a few ma of current before they saturate.This transformer is wound on a VAC 250F core. This core has permeability that is much reduced from the VAC 500F core used in the B-WIT-100 transformer and will tolerate much more current before the onset of saturation.The tradeoff is reduced band width, mostly trimmed off the LF end of the scale.My impression is if you want to focus in on the LF use a different transformer. If you want to put the secondary of this transformer in series with the power supply to your audio amplifier to test PSRR this just might be the transformer to use.This transformer is wound on a VACUUMSCHMELZE T60006-L2040-W964-02 250F core. There are 40 turns of CAT 6 plenum solid twisted pair.@rx8pilot,Thanks for sharing your approach to learning this stuff. You can look at all the various equipment user’s manuals, they don’t take much space to explain the interworking of stuff. The best single source I can recommend today is “Power Integrity”, Measuring, Optimizing, and Troubleshooting Power Related Parameters in Electronics Systems by Steven M. Sandler.https://www.amazon.com/Power-Integrity-Optimizing-Troubleshooting-Electronics/dp/0071830995/ref=sr_1_1?s=books&ie=UTF8&qid=1534877929&sr=1-1&keywords=power+integrity. Cheep at$16.00DT

author: capt bullshot
author_rank: Super Contributor
timestamp: August 21, 2018, 07:24:27 pm
content: From the frequency / phase response, I suppose you've used a rather low termination resistor for this transformer? This core has a quite low A_L (2.3uH @ 10kHz), so I'd expect a higher low frequency cutoff if it was terminated to 50 Ohm.For comparability, you should specify its value.

author: DualTriode
author_rank: Contributor
timestamp: August 21, 2018, 07:31:24 pm
content: Thank you.For this plot the resistor is the 50Ohm resistor internal to the Bode 100.Same as Dave used in the video.DT

author: capt bullshot
author_rank: Super Contributor
timestamp: August 21, 2018, 07:45:32 pm
content: Okay, thanks, still wondering. Doesn't match my experience with my home rolled transformers and the 3577A. I vaguely remember the Omicron having a "low impedance mode" for its output. What was the used source impedance? My 3577A has 50 Ohm output impedance, in case the Bode 100 was switched to something else, this might explain the difference.Edit: did you measure "source" to "transformer output" ratio (including the source impedance into the measurement) or "transformer input" to "transformer output" (using two inputs of the VNA, excluding the source impedance)? I believe this is the reason for our different results, as I've done all the measurements the first way (using only one input).BTW: didn't watch the whole video (sorry Dave), I do prefer reading stuff over watching videos

author: DualTriode
author_rank: Contributor
timestamp: August 21, 2018, 08:30:49 pm
content: Oops!capt bullshot,You were correct, I did not have the 50 Ohm output switched on. I switched on the 50 Ohm output and ran the plot again, this time down to 1 Hz.The LF response was not noticeably changed. The HF response was slightly improved.I will lug the 4395A VNA to the bench and run the plots on that VNA and post here.Thanks DT

author: rx8pilot
author_rank: Super Contributor
timestamp: August 21, 2018, 09:20:13 pm
content: Quote from: DualTriode on August 21, 2018, 07:11:14 pmI actually met him at a trade show and purchased the book right there. It has been an excellent resource! There are, however, plenty of details that are hard for me to absorb without sitting at the bench and doing the work. Now that I have the gear, I have run out of excuses and just need to dive into the deep end. Sandlers book and all the other resources I have gathered are just now starting to make sense.Quote from: capt bullshot on August 21, 2018, 06:53:33 pmThank you....excellent information!

author: DualTriode
author_rank: Contributor
timestamp: August 21, 2018, 09:49:45 pm
content: rx8pilot,It is easy to make a mistake. I suggest that you check all the connections with a volt meter to confirm that the voltages are safe for your expensive test equipment. It is easy to vent the magic smoke.Thanks DT

author: rx8pilot
author_rank: Super Contributor
timestamp: August 21, 2018, 10:18:07 pm
content: Quote from: DualTriode on August 21, 2018, 09:49:45 pmThe low-frequency operation makes AC coupling a challenge - I hope I can avoid blowing up my box. The HP 3577A has fairly decent overvoltage protection, but obviously, it has limits.Measuring passive components is pretty safe, but doing FRA introduces a considerable risk of smoke. Not sure what the Bode 100 has in terms of input protection other than user selectable attenuators.

author: precaud
author_rank: Frequent Contributor
timestamp: August 22, 2018, 02:24:44 am
content: Quote from: rx8pilot on August 21, 2018, 06:16:57 pmAh, I totally appreciate that. Previous advice given by others is very good. My uses tend more toward FRA than VNA, so I'll only add, I find it extremely useful to have a set of components (R's, C's, L's) that cover a wide range of values, which I have measured on other devices to compare my results to. "Confidence by Consensus".Definitely put together a set of DC blocking cap fixtures for your 3577A. It's not a chance worth taking.QuoteI'd skip the stuff in AP's manuals about impedance measurement, it's pretty unsophisticated. They only cover the "Series-R" topology and do nothing to measure and remove residuals, which is necessary for good results.

author: rx8pilot
author_rank: Super Contributor
timestamp: August 22, 2018, 03:29:48 am
content: What kind of LF response do you target with your DC blocks?Short and misplld from my mobile......

author: precaud
author_rank: Frequent Contributor
timestamp: August 22, 2018, 03:58:35 am
content: The 3577A low freq limit is 5Hz, so something below that. 100nF into 1MOhm gives -3dB a tad over 3 Hz. Scale to taste...

author: rx8pilot
author_rank: Super Contributor
timestamp: August 22, 2018, 04:16:20 am
content: Oh, of course! I was fixated on 50 Ohm which is a totally different thing, lol.For FRA, the receivers will (likely) always be 1M. That is when the system is in the danger zone..... connected to all kinds of power supplies where DC blocks are needed.Does anyone know if the Bode 100 has AC coupled inputs? It did not look like it after scanning the brochure.Short and misplld from my mobile......

author: precaud
author_rank: Frequent Contributor
timestamp: August 22, 2018, 12:12:10 pm
content: Quote from: rx8pilot on August 22, 2018, 04:16:20 amI'm pretty sure it does. They demo the "shunt-thru" impedance technique, which requires 50 Ohm term on both channels, without adding an external term.

author: precaud
author_rank: Frequent Contributor
timestamp: August 23, 2018, 12:52:50 pm
content: Quote from: rx8pilot on August 21, 2018, 06:16:57 pmThis app note from AP is more useful than their manual:http://u.dianyuan.com/upload/space/2010/10/29/1288318638-361233.pdfThe AP200 shown is the same as my 102B except it interfaces to the computer via a parallel port.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 12:01:06 am
content: Quote from: EEVblog on July 13, 2018, 11:14:53 amHi Dave,I was wondering what is so special with the Omicron B-WIT100 from your teardown transformer, and I was able to duplicate the transfer characteristics using two stacked cores from Vacuumschmelze (VAC), PN T60006-L2030-W514. The result are almost identical (all was measured on a Keysight E5061B-3L5 I now have on a test loan).The big difference is the cost: My transformer is about 60 to 70€ including the box, the Omicron is about 500€ incl. VAT.All the nittigritti is documented here (at the bottom):https://electronicprojectsforfun.wordpress.com/injection-transformers/

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2018, 12:10:20 am
content: Quote from: Wolfgang on October 04, 2018, 12:01:06 amI am VERY thankful for this write up @Wolfgang!.It so happens that I have the exact same core sitting on my bench and it is about to become my new injection transformer.Not sure why this is so interesting and fun.....but it is.Off to do some winding now.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 12:31:41 am
content: Do you want the STL for the holder ?

author: precaud
author_rank: Frequent Contributor
timestamp: October 04, 2018, 12:56:16 am
content: Quote from: Wolfgang on October 04, 2018, 12:01:06 amOne heckuva job, Wolfgang!

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2018, 01:21:25 am
content: Quote from: Wolfgang on October 04, 2018, 12:31:41 amFor sure, I don't have a 3D printer but I can CNC machine it from Delrin.I will probably machine a case for it and give it a fun name: NVT-1Nude Virgin Transformer - 1

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 01:44:57 am
content: ... for all interested: I uploaded the STL file of the holder in a ZIP and the webpage has the link in it now.Have fun !Wolfgang

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2018, 01:57:55 am
content: Thank you so much, this is a great project.Short and misplld from my mobile......

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 02:01:10 am
content: Quote from: rx8pilot on October 04, 2018, 01:21:25 amNVT1 - A Good name, why not. I'll make a label for it tomorrow.Delrin is the same as POM? I like it too but the electrostatic chips when milling drive me nuts. There is no place where they dont stick to.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2018, 03:10:21 am
content: And for the graphics.....

author: DualTriode
author_rank: Contributor
timestamp: October 04, 2018, 05:06:38 pm
content: Wolfgang,Such pride?Been there done that.The VAC T60006-L2030-W514-03- core appears to be an exact match for size and color for the core in the real B-Wit injection transformer.See Reply #79 for a photo.See Reply #96 for a plot (identical to the real deal)It all fits into a cute little Hammond box just like the real deal.DT

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2018, 06:33:19 pm
content: Quote from: DualTriode on October 04, 2018, 05:06:38 pmNow, now.....The write up by Wolfgang is really nice....and seeing some of the initial efforts is very interesting.Quote from: DualTriode on October 04, 2018, 05:06:38 pmThis is exactly why I already have one on my bench....I put it in my next Mouser order. Good work, thank you.Quote from: DualTriode on October 04, 2018, 05:06:38 pmDo you have this plot scaled by chance? The db/div and deg/div are rather course in the range of interest. Not too critical, but the conversation has been splitting hairs and the precision of your plots are bigger than a hair.Back to one of the earlier questions.....Why does the response need to be so flat and phase perfect when the calibration of the VNA can null out the transformer response?Are nude virgins actually helping here?

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 06:39:26 pm
content: Quote from: DualTriode on October 04, 2018, 05:06:38 pmHi,I disagree that it is the same core.The datasheet of your part is here:https://www.vacuumschmelze.de/fileadmin/Medienbiliothek_2010/Produkte/Kerne_und_Bauelemente/Anwendungen/Kerne/Kerne_SKDs_Kunststoff/W514.pdfthe core in my B-WIT100 (I disassembled it today to check) has a diameter of 42mm.Maybe they changed the core during production, I dont know.The internals of the box I did not like so much. Its all antistatic mats and glue, the fuse is soldered and insulated by shrink-wrap, only one side is fused, ...Not a convincing expression of quality, for 500€, I would say. So the real deal is not exactly a good deal.To make my own was a challenge and a prank. I do know its not rocket science, and it was just a fun thing. See last photo on my "injection Transformers" page.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 07:02:26 pm
content: Hi,the reason why you should not rely on nude virgins but rather have a good injection transformer is measurement accuracy. It is correct (it was the prime argument of the Texas instruments people in their Bode papers) that the transformer can be normalized out, but:- the problems occur at the band corners, where the S21 of the transformer deviates from 1 a lot (e.g., 10dB for the B-WIT100 at 1Hz).Lets say we are at the low frequency range (there its most prominent) for now.- your injection amplitude is now 10dB down, say, i.e. your measurement noise goes up- If you try to increase drive level, you will soon run into core saturation problems creating harmonics and all other kinds of dirt effects.The lower the frequency gets, the more pronounced this problem is. Dont forget that allowable DC-AC current to avoid saturation is in the range of 10mA.- At the high frequency edge stray inductances and interwinding capacitances could make your measurements problematic, because the parasitic elements arenormally not very well known.So, transformer imperfections can be calibrated out, but at the cost of less dynamic range.I think what we got here is about the max that can be expected from a single-transformer design.When you look at the market, they have special transformers for the low end (Ridley, Picotest, Omicron, ...) with heavy cores. Their high-end behaviour is bad, however. The small cores do it just the other way. It only depends what you need.Techniques that could work (I never tried, just saw some literature) are stacked transformers, each for its own frequency band, ...)To make this is extremely tricky, involves extended alignment and compensation and you can be glad to get a factor of 10 in frequency range over normal cores.

author: ogden
author_rank: Super Contributor
timestamp: October 04, 2018, 07:13:21 pm
content: Quote from: Wolfgang on October 04, 2018, 07:02:26 pmAre you really not sure about your DC supply stability below 1Hz? Or even 100Hz?

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 07:21:16 pm
content: Hi,what I hear the problems at low frequencies are a peculiarity of the PFC (power factor correction) people. Dr. Ridley has a video about this; they attack a PFC regulator by imposing strong sub-Hz disturbances and then check if the PFC IC still works. For normal linear PSUs, LF instability is not likely to occur because most PSU at least are good enough to suppress rectified line ripple, around 100Hz in Europe. Switching regulators with several regulating loops working parallel are a different matter. There testing LF also makes sense.

author: DualTriode
author_rank: Contributor
timestamp: October 04, 2018, 07:56:27 pm
content: Apologies,Back on June 7th I opened the B-WIT-100 and measured the core inside and went to Mouser to see if I could find the part. I just looked up the part that I ordered and used to make the Home Roll transformer is this one:https://www.mouser.com/datasheet/2/599/W424-237924.pdf. In error I posted the wrong part number in Reply #79.The photo and plot are the correct items.In terms of plots with a finer scale what I posted is what you get from the Bode 100 software. The Bode 100 and software does record precise data points that will split fine red hair.All the conversation about gain and phase at the tails of the plots I believe is mostly arm waving. The Bode 100 or for that matter any VNA will do Thru calibration and correct for a moderate degree of Phase and Gain variation.Again I am sorry for posting by mistake the incorrect part number, this is the part in the photo and tested and appears to be very close to the B-WIT-100 core.https://www.mouser.com/datasheet/2/599/W424-237924.pdfThanks DT

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 08:22:14 pm
content: Dont worry, many ways lead to Rome.One should not forget that the cores have tolerances of a few 10 percent up and down. The difference between the homebrew curves and the B-WIT100 are probably less than the average variation between different B-WIT100 units.The core you used has an average Al of 109, the one I used has one of 94. The mouser part number you gave has no plastic trough filling around it as mine and the one used in the B-WIT100. I know that only german readers can identify this difference. So maybe you got yourself a similar, but not the same part.I am not completely in agreement with the idea that the Bode 100 will kill *all* problems. For PFC, there are probably better (sub 1Hz) machines, and for ultra-high frequency switchers you probably need another lineup of injectors. I have no big trust in banana wired setups at 50MHz. Another field where I have not worked myself in sufficiently yet is the measurement of really small impedances like PDNs on digital boards.At the moment I am testing the E5061B-3L5 and the Bode 100 in parallel and the agreement at low frequencies is good (10MHz). Above that I would believe the E5061B-3L5 a lot more (upper limit is 3GHz). But - no final results here yet.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2018, 08:28:35 pm
content: @Wolfgang HA!Funny.....

author: ogden
author_rank: Super Contributor
timestamp: October 04, 2018, 09:18:03 pm
content: Quote from: Wolfgang on October 04, 2018, 07:21:16 pmOh, PFC people. They are supposedly rich, right?- I would say that sub-1Hz job is not easy for transformer. To cover low frequency range down to DC one could tryisolation amplifierbased "injection transformer"

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 09:29:53 pm
content: ... the video shows a transformer that has a few 100g (Dr. Ridley *weighs* them as a criteria for quality) and then he weighs all the others (and concludes that they are too light for the hard job). Irony apart, of course you could always throw some kilograms of iron and copper at any LF problem it will work. It wont be cheap, however, and an independently powered solid-state injector could be a better option. There are quite some on the market.Whatever you see at Ridley, Omicron, Picotest or Keysight is made to make their own products shine. Independent thinking is key to not fall into a vendors honeypot. The matter is tricky, there are many pitfalls, and a lot of info is not very well communicated. Lots of work to do !

author: rx8pilot
author_rank: Super Contributor
timestamp: October 04, 2018, 09:44:17 pm
content: When Ridley got out the scale, I almost fell out of my chair.All I really care about is how it performs in real life - it was really unexpected from a person with his pedigree and credentials. That type of sales pitch really degrades his own line of products for me.And yes, for the really low frequencies - a solid state solution is a clear winner in performance at that expense of complexity.

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 09:50:47 pm
content: The Omicron people have their own videos where their products shine and Ridleys dont (no surprise, the focus on bandwidth and flatness, where the big super-LF stuff flunks out in the 10kHz range). There is no such thing like a single size that fits all. Check what you really need, try all yourself and let the salesmen talk as much as they may.

author: Bud
author_rank: Super Contributor
timestamp: October 04, 2018, 10:53:15 pm
content: Quote from: rx8pilot on October 04, 2018, 06:33:19 pmIn general you want errors to be as small as possible to reduce dependency on stability of calibration, because of time or temperature changes,etc.

author: Bud
author_rank: Super Contributor
timestamp: October 04, 2018, 10:57:48 pm
content: Quote from: rx8pilot on October 04, 2018, 08:28:35 pmYou can bet someone is about to get offended and , given the placement of the transformer symbol, ask what do you mean by "injection"

author: DualTriode
author_rank: Contributor
timestamp: October 04, 2018, 11:12:50 pm
content: One size does not fit all.The high permeability cores saturate easily with only a handful of ma’s current. This one I used a much lower permeability core and tested inductance with up to 100ma with no sign of saturation. The lower permeability also results in less LF performance. (tested with Rhode HN8118 LCR meter)This injection transformer is intended to be in series with the power supply and test audio amplifier PSRR.I have misplaced the APx555 output plot.DT

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 11:38:44 pm
content: Quote from: Bud on October 04, 2018, 10:57:48 pmIMHO, its a harmless prank, and the words came from the master of all this forum himself, Dave.The picture is a classic Amadeo Modigliani, and no obvious sexuality is shown.This is art, not porn.Smut is in the eye of the beholder (Tom Lehrer).

author: Wolfgang
author_rank: Super Contributor
timestamp: October 04, 2018, 11:44:00 pm
content: The plot would say more with a proper scale (1dB/div) for gain.The problem with high-mu cores saturating with small DC currents is well known.Two ways out exist:- lower mu, with worse LF response as a consequence- dont change core, but let no DC go thru it by using a huge blocking cap.There is some Keysight literature about how to do this.What is the frequency range you would like to cover ?

author: DualTriode
author_rank: Contributor
timestamp: October 05, 2018, 12:33:38 am
content: No Problem.This transformer demonstrates that one size does not fit all.It is installed at the output of a DC power supply.The frequency range is from below 10hz to mid Mhz range.This transformer will test Amplifier and Power Supply Rejection Ratio.DT

author: Wolfgang
author_rank: Super Contributor
timestamp: October 05, 2018, 12:39:07 am
content: Hi,just a hint: you could do it in two sweeps, with the LF part covered by a fat transformer (Omicron, Ridley, Homebrew by stacked cores, ...)and a normal transformer for the higher frequency part.Just a question: Why are you testing up to a few MHz ? Are you afraid of amp instabilities of RFI problems ?Do you want to try a core that withstands a lot of DC current or by the Keysight method with a DC block cap so the transformer always runs in AC mode ?How many amps does your supply current have ?

author: DualTriode
author_rank: Contributor
timestamp: October 05, 2018, 02:38:01 am
content: Hello,I want to keep this as simple as possible and only add complexity as needed. Audio Precision uses a Jensen JT-123-BLCF transformer for this application in their technote 106 (you need to sign in at the AP.com site to download the technote).https://www.ap.com/download/technote-106-measuring-psrr-power-supply-rejection-ratio-2/?wpdmdl=5795I am looking for a transformer that will withstand maybe 200ma or 300ma, so far 50ma is enough. I have used this transformer with a 12B4A audio tube amp tube circuit biased to ~ 35ma. The 12B4A will oscillate if you give it a chance.Why test to a few Mhz? Afraid? No. Yes I am looking for wider bandwidth than the Jensen transformer. I do want to take a look for RF and possibly other oddities even oscillation. Mostly it is fun to look.I am not opposed to the Keysight method. Perhaps you can supply a reference. I do have Keysight instruments on the bench and Keysight books on the shelf.Thanks DT

author: Wolfgang
author_rank: Super Contributor
timestamp: October 05, 2018, 10:33:03 am
content: Quote from: DualTriode on October 05, 2018, 02:38:01 amSome comments to that:- Your Jensen transformer covers the audio range only, and one winding (of 4) has 20 Ohms already. I have missed a DC current tolerance spec in the datasheet.- it could well be that even a moderate DC current of a few 10 mA drives it into saturation so much that the inductance goes down a lot.- What you might need is an output transformer for tube class A linears. They are used to DC bias.- Info about some Keyside tricks can be found here:http://literature.cdn.keysight.com/litweb/pdf/5990-5902EN.pdfhope that helps because 10Hz to a few MHz with up to 300mA DC - thats a challenge.Wolfgang

author: MilkmanCDN
author_rank: Contributor
timestamp: October 18, 2018, 11:53:18 pm
content: @DualTriode,Thanks for updating the correct BWIT transformer part number. In my haste I ordered 3x of the wrong one and was wondering why I could only get 30 turns around the transformer, instead of 40. Looks like the correct transformer is a little larger. It's all making sense now. New order placed.

author: Relaxe
author_rank: Regular Contributor
timestamp: October 23, 2018, 08:40:25 pm
content: Thanks for your work Wolfgang!Can you tell us the part # of the Hammond Box?I want to duplicate this here...

author: Wolfgang
author_rank: Super Contributor
timestamp: October 23, 2018, 10:58:22 pm
content: Hi,I am not a home at the moment, but I think it was a 27134PDLA Hammond / Eddystone series box.If you wait until monday I can look it up to be 100% sure.RegardsWolfgang

author: Relaxe
author_rank: Regular Contributor
timestamp: October 24, 2018, 01:58:06 pm
content: Thanks,As the 27134PDLA is not available at Digikey/Mouser, I will fit it in the dimensionaly similar 1590T.About the Fuse: I have selected LittleFuse 0251001.NRT1L . Does the series resistance (0.128 Ohms) affects the circuit?About the injection resistor, I have seen documentation claiming the resistor must match the transformer impedance. Picotest’s J2101A recommend a 5 Ohm resistor. What do you recommend?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 24, 2018, 02:10:38 pm
content: As seen in the rest of this thread -- lower load resistance extends LF response, at greater expense to the HF response. HF response is most when source and load are matched; but you may not need this range, so that may be an acceptable tradeoff.The load resistance is usually made low so that it does not interfere with the circuit it's introduced to.Tim

author: Wolfgang
author_rank: Super Contributor
timestamp: October 24, 2018, 07:27:34 pm
content: Quote from: Relaxe on October 24, 2018, 01:58:06 pmHi,I bought mine at Conrad electronics (I found an old email). I dont know if you have something similar in Canada. The box does not really matter. Now for the fuse: The allowable DC current for the high-mu cores is very small, in the range of 10mA. The fuse is just there to prevent destructions by dead shorts. The wire resistance of the windings is a few 100Ohms so I see no issue with the fuse resistance. In total we are way below 1Ohm.best regardsWolfgang

author: Relaxe
author_rank: Regular Contributor
timestamp: October 26, 2018, 08:13:39 pm
content: I just did mine,Here's the BOM, using Mouser parts:2x 983-T60006-L2030W5142x 576-0251001.NRT1L1x 546-1590T1x 530-108-0903-11x 530-108-0902-11x 571-5-1634523-11x 71-AVE030020E16R0KEoptionnal: 1x 372-U1163AI used less than 3m of twisted pair wire from a CAT7 patch chord I had laying around.Total cost: 95 Canadian $.Did not test yet, but posting to share the love.Thanks again Wolfgang!

author: Wolfgang
author_rank: Super Contributor
timestamp: October 26, 2018, 08:41:47 pm
content: Cool ! The little green things are fuses, am I right ?Curious for the measurements now, of course !!RegardsWolfgang

author: _Wim_
author_rank: Super Contributor
timestamp: October 27, 2018, 12:17:50 pm
content: I also made a couple of these in a while ago posted about them here (including measurements):https://www.eevblog.com/forum/testgear/looking-for-a-low-cost-way-of-measuring-dc-dc-converter-control-loop-response/msg1738013/#msg1738013

author: Wolfgang
author_rank: Super Contributor
timestamp: October 27, 2018, 02:09:54 pm
content: Thanks, I've already seen tham. Good site !

author: MilkmanCDN
author_rank: Contributor
timestamp: November 07, 2018, 01:31:35 am
content: Curious, what's the rating on the fuses that you used? I'd assume it's fairly large (>1A) as we're only trying to prevent wires from over-heating during transformer saturation.

author: Relaxe
author_rank: Regular Contributor
timestamp: November 29, 2018, 01:16:32 am
content: Hey guysI finally got around using the thing.I installed the demo of Frequency Response Analysis option for the DSOX3000T scope. It uses the onboard signal generator and scope probes to do the magic.To qualify my NVT-1, I plugged a BNC from the WaveGen to the VNT-1 Input, and both scope probes to the VNT-1 output.Looks like a pretty flat response!I attached the image of the plot, setup, and the .CSV of the results.@MilkmanCDN: I Used 1 Amp fuses. See Mouser part#.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 29, 2018, 01:59:03 am
content: Quote from: MilkmanCDN on November 07, 2018, 01:31:35 amYes, I used a few 100mA IIRC. The purpose is to prevent buring the wires. The core will saturate way before that will happen.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 29, 2018, 02:00:49 am
content: Quote from: Relaxe on November 29, 2018, 01:16:32 amLooks fairly flat and OK to me ! And now much fun with the virgins !

author: DualTriode
author_rank: Contributor
timestamp: November 29, 2018, 06:28:12 am
content: Nice scope.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 02, 2018, 01:52:16 am
content: I finally got mine wound up and made a signal splitter for my HP 3577A. Still, I need to add some AC coupling on the inputs.I think I am now set up for a new SMPS design I am building.

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: December 09, 2018, 02:11:15 pm
content: Quote from: capt bullshot on August 21, 2018, 06:53:33 pmHiI had planed to rebuilt the HP 35676 but I have some questions regarding it's operation as described in the manual.First of all, if I look at this schematic, it seems to me that the 80R6 is the current sensing shunt resistor. The rest is pretty much a ~13dB T-attenuator for the reference input and a ~9dBm T-Attenuator on the voltage sensing A input. At least that is what I first thought.But when I read the manual, I see that for one port measurment the A/R and for 2-port the B/R functions are applied. So this would mean measurements of "V" "only"(?) In this case I assume the 80R6 resistor is used to match the two T-Attenuators which don't seem to have a 50ohms input impeadance on their own.But, what if one would like to do V/I measurments? Could I use the 80R6 resistor as a shunt like I first thought and measure voltage over the DUT on the A port, and current trough the DUT via R-B measurment and terminate the DUT either in 50ohms / B input for a 50Ohm system or lets say at ground for a capacitor / inductor with =/ 50ohms?

author: capt bullshot
author_rank: Super Contributor
timestamp: December 09, 2018, 06:11:57 pm
content: Quote from: sixtimesseven on December 09, 2018, 02:11:15 pmDon't know if I can answer your question to your satisfaction. Afaik, the 35676 is just a voltage divider (the said 80R6 vs. the input impedance of the DUT). So the 3577 can measure the ratio of A to R and calculate the DUT's impedance within a limited range. There's no way to directly measure the current through the DUT.

author: MilkmanCDN
author_rank: Contributor
timestamp: January 25, 2019, 04:42:04 pm
content: Folks,I finally finished putting my isolation transformer together. Took a little longer than I would have liked, and Dave is bang on regarding $500 being an acceptable price. Researching/purchasing all the right bits/pieces, winding the transformer, and testing took me quite a few hours.My bill of materials is:Fuse Holder - $3.99 USD (10 pieces)https://www.aliexpress.com/item/10PCS-5x20mm-Black-AGC-Fuse-Holder-Inline-Screw-Type-with-18-AWG-Wire-for-Car-Auto/32386078437.htmlSlow Blow Ceramic Fuse Kit - $7.98 USDhttps://www.aliexpress.com/item/100PCS-Slow-Blow-Ceramics-Fuses-Kit-In-Box-5x20mm-T-1A-2A-3-15A-4A-5A/32860583104.html1590B Guitar Stomp Box - $4.24 USDhttps://www.aliexpress.com/item/TSAI-1Pcs-Guitar-Stomp-Box-Effects-1590B-1590A-Style-Aluminum-Pedal-Enclosure-for-Guitar-sell-Popular/32827672144.htmlWiring Terminal (for chassis ground) - $18.90 USD (10 pieces)https://www.aliexpress.com/item/M6-23mm-Copper-wiring-terminal-All-metal-grounding-column-with-4mm-Banana-jack-plug-hole-10pcs/32770586031.htmlAdhesive Insulation Foam (10mm thick) - $1.80 USD (1 sheet)https://www.aliexpress.com/item/30-x-50cm-Car-Adhesive-Sound-Insulation-Cotton-Foam-Thick-Soundproof-Rubber-Car-Noise-Insulation-Foam/32864585299.htmlRed/Black Banana Socket - $3.66 USD (includes 5x Red and 5x Black)https://www.aliexpress.com/item/Hot-Selling-10Pcs-4mm-Banana-Female-Jack-Socket-Panel-Mount-Binding-Post-Connector-2Colors/32845561917.htmlInsulated BNC Connectors - $4.85 USD (10 pieces)https://www.aliexpress.com/item/Sale-10-Pcs-Copper-BNC-Female-Isolated-Bulkhead-Mount-For-RF-Radio-Adapter-Connector/32512098437.htmlCAT6a Ethernet Cable (14 ft) - ~$10 USDI had one of these lying around. I cut the ends off and used. 23AWG stranded wire.Blue Paint - ~$7 CADNot required, but I picked up a can of metal spray paint from Home Depot.Transformer Vaccumschemelze T60006-L2040W424- ~$40 USDhttps://www.mouser.com/ProductDetail/vacuumschmelze/t60006-l2040-w424/?qs=ePbE9GiMmvVbc%252bVKk8tsZw%3d%3d&countrycode=US&currencycode=USDTHANK YOUtoDualTriodefor identifying this as the same transformer used in the BWIT-100Avery Sticker Sheets (6468 template) 2"x 4" Labels - ~$10 USDI had some of these lying around.I reduced the cost of the transformer by building multiple (x3) as a couple of friends wanted one. I estimate that the cost of materials to construct is around ~$65 - $80 USD per transformer. I've got around 10-20 hours into this project.I've attached a copy of the Visio diagram that I used to create both the drill templates and stickers.Pictures of the unpainted metal boxes, drilled boxes, internal components, and finished transformers are attached. I decided to call the transformer ANVT-100 as a play on Dave's review. I did test these transformers using a scope/function-generator and performance is right in line with what has been previously posted here. When I get a chance, I'll circle back and post a proper bode plot from the Venable at the office.A big thanks to all on this forum. Especially Wolfgang and DualTriode for sharing their build and test details. Lot's of great information here and really helpful folks.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 28, 2019, 12:17:00 am
content: Chapeau ! Looks VERY close to the original. I find my nude virgin label more attractive, however.Why you have just *one* fuse ?Wolfgang

author: MilkmanCDN
author_rank: Contributor
timestamp: January 28, 2019, 06:26:28 pm
content: Thanks Wolfgang,I only put one fuse because it's typically the driving side (BNC input) that injects current. However, given that the transformer could be used in both directions, and the secondary can also be subject to higher currents, I suppose putting one on both sides would be prudent. That said, the original BWIT-100 only has a fuse one-side as well.I also think your label is much more attractive; however, it's resemblance to a famous internet meme (think goats), might get the box banned from my household. I'm pretty sure my wife wouldn't approve.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 28, 2019, 07:02:31 pm
content: ... in the end, its a classic piece of art by Modigliani recently sold for more than 100 million at Sotheby's.Its undisputably *art*, nothing else. Be strong and defend the liberty of free expression !!You know what: an engineer from Omicron had a burst of laugh when he saw it - these people are OK, and their sense of humour is OK too.

author: precaud
author_rank: Frequent Contributor
timestamp: January 28, 2019, 08:22:08 pm
content: Quote from: Wolfgang on January 28, 2019, 07:02:31 pmThat is my impression of them, too.

author: MilkmanCDN
author_rank: Contributor
timestamp: February 08, 2019, 10:17:12 pm
content: Quote from: Wolfgang on January 28, 2019, 07:02:31 pmI see what you did there.

author: Wolfgang
author_rank: Super Contributor
timestamp: February 08, 2019, 10:40:02 pm
content: Honi soit qui mal y pense.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 13, 2019, 12:10:11 am
content: Hi group,I see a lot of people have winding their own NVTs. I want to share an alternative approach.You simply buy the B82720H0015A035 EPCOS (TDK) from Digikey. They cost $2.66 USD or $3.66 CDN.This part is quite small:Here is the spec:The magnetizing inductance is 68mH, not as high as the NVTs, but still quite high. The leakage (stray) inductance is 1200nH.In a 50test circuit:The modelling results show a 3dB bandwidth from 60Hz to 13 MHz.The model does not include any capacitance.Measured results:The low frequency 3dB point is 50 HzThe high frequency 3dB point is 4MHz.The transformer does not have to be flat in the normal control loop measuring scheme.This common mode choke, used as a transformer, is suitable for most power supply control loop analysis.Regards,Jay_Diddy_B

author: Wolfgang
author_rank: Super Contributor
timestamp: February 13, 2019, 01:07:08 am
content: Hi,why not ? If you can live with the bandwidth restrictions, its a cheap alternative. The cores I used cost some 10€ each.Thanks !Wolfgang

author: precaud
author_rank: Frequent Contributor
timestamp: March 06, 2019, 02:55:09 pm
content: This thread has become more about transformers than the Bode 100, so I'll continue in that vein.I've been meaning to make a 2:1 stepdown version of this, optimized not for control loop response but for making low-impedance measurements. The major difference is that the xfmr is working into a load defined as (1 Ohm + Zdut). For a 1:1 xfmr this results in a very restricted bandwidth, easy to saturate at low freqs, and other problems. I finally got around to making it Monday.Prior to this, I've only put together 1:1 xfmrs so I wasn't sure how best to do different winding ratios. I was certain that I didn't want the windings in separate layers; reasonably certain that I wanted to use twisted-pair conductors for extended HF bandwidth. But beyond that, how best to arrange the remaining windings was not clear. What I ended up doing is first winding the 40-ish turns with the conductors in twisted-pair config, and then adding the additional primary turns as an outer layer. (Maybe they should have been the inner layer?) I have a spool of 22 ga. magnet wire on hand so I used that. The result was 88 turns for the primary, and 42 for the secondary, wound on a VAC T60006-L2030-W423 core:https://www.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2030-W423?qs=sGAEpiMZZMs2JV%252bnT%2fvX8PvC43ppqs%252bkNLW11zNOYmc%3dThe point of the stepdown is to maintain wider bandwidth with less loss while driving low-impedance loads. My goal is to get a -6dB bandwidth of 1MHz into 1 Ohm. We'll see how that worked out...The plot shows the freq response of the xfmr terminated in 50, 10, and 1 Ohms. (The messiness above 10MHz is due to the long xfmr leads and unshielded clips used in the test setup. This will clean up in the final install. I'm not focused on the response up there... yet.)For comparison, I've included the same plot for one of the better 1:1 50 Ohm xfmrs I've used in this application, a North Hills 0016PA 50 Ohm isolation xfmr.Comparing the traces, you can see the homemade xfmr does indeed do a better job of driving the lower loads with less loss and wider bandwidth, at the cost of about -7dB stepdown loss. Compared to the 0016PA, -3dB bandwidth is about doubled into 10 and 1 Ohm loads; 240kHz into 1 Ohm, -6dB at just shy of 500kHz. This is headed in the right direction, but still short of the 1MHz goal.On the low end, response is excellent, less than 1dB down at 1 Hz, and doesn't change appreciably with load.So, two questions. It appears I'll need to use a 3:1 winding ratio to get the desired bandwidth into 1 Ohm, yes?What's the best way to interleave/layer the windings for maximum bandwidth?Any input would be appreciated.

author: capt bullshot
author_rank: Super Contributor
timestamp: March 06, 2019, 03:22:48 pm
content: I'd try to wind it tri- or quadfilar and then connect two or three of the resulting windings in series for the primary.Some time ago, I made a silly attempt to make a multi-core "coaxial" transformer - put five wires into a shield, wind a transformer from that and connect the wires in series. Don't have pictures and no spare time to provide some at the moment, but afair the result was impressive in terms of stray inductance but _not_ too impressive in terms of frequency response into higher impedances (I tested it as a step-up transformer, not a step-down). Would be interesting to test that thing into low impedance again.Edit _not_

author: precaud
author_rank: Frequent Contributor
timestamp: March 06, 2019, 03:45:27 pm
content: QuoteI had thought of doing that, but nixed it and can't remember why... maybe cuz the twisted configs maintain more consistent impedance over a wider BW. I'd also considered a braid but that's tedious... 40 years ago my GF braided two 10-foot 3-cond cables using 16 ga... no complaints, bless her heart... she said it was smaller than the hair bundles she normally worked with

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 07, 2019, 01:10:55 am
content: To get infinite bandwidth on a ratio, you need a Guanella TLT.The principle is using TLs in series-parallel combinations at each port, so that the signal sent down each TL is exactly the right fraction of the total, in exactly the right impedance, so that the waves are put back together exactly in phase, no delay shift. Ultimate bandwidth is limited by the cross section of the TLs, the routing in the port area, and crosstalk between TLs (because, of course, no TL is ideal with infinite common mode impedance).To get maximum (note, it will always be finite) bandwidth on an isolating transformer, you basically want 1:1. Other ratios are effective, but you will have some compromise between a Guanella style construction, a Ruthroff type (where fewer TLs are used and the delays are unmatched), and a conventional (not-TL-driven) design.For example, consider the 1:N transmission line transformer, where a signal line is routed along a reference plane multiple times. The plane forms a slotted loop (it might be a cylindrical shell made of copper sheet or foil, or a planar circle on a PCB, say), while the signal forms a spiral or helix (or equivalent). The slot in the plane, in turn, connects to a parallel plate transmission line.A cylindrical example looks like thus:The "signal" line here is 1/8" (3.1mm) copper tubing (with sleeving), bifilar, inside a sheet metal surround. The transmission line impedance I would guess is on the order of 50 ohms (per signal line). The output line should be around 9 ohms.The delay through the signal line is N turn lengths, while the delay through the plane is just one turn length. If a step change in voltage is applied to the plane, that voltage is induced on the signal line, simultaneously, at each point the line crosses the plane split. When this propagates out to the terminals, the result is a series of N steps (of complementary polarity from each end of the line, with respect to the reference plane).The signal is always with respect to a reference plane, so it's balanced, and each end of the winding has that same reference. This is good when you need a balanced signal, but when you need isolation, you need imbalance -- the delay of the signal line corresponds to the equivalent isolation capacitance and leakage inductance in the transformer.Any construction that is similar to this, will get you pretty good bandwidth.You can apply the same theory to conventional (multilayer) windings, as well: in that case, each layer of turns is the reference plane for the layers nearby, and so on, so the characteristic impedance of a multilayer (per segment) winding can become quite high indeed (to first approximation, the impedance is the impedance of how many turns tall+wide it is). Predicting what happens in cutoff, in windings like this, who knows -- but estimating where the first cutoff is, isn't so bad!Incidentally, the characteristic impedance of a common mode choke like this,https://www.digikey.com/product-detail/en/taiyo-yuden/TLF9UA102W0R8K1/587-2788-ND/2573875is around 600 ohms. There's a few layers in there, and the two windings are rather poorly coupled to each other! The resulting bandwidth is even lower than you'd expect given the wire length (which probably isn't much on a small one like this, though I haven't counted). The isolation capacitance is quite low, though.Tim

author: precaud
author_rank: Frequent Contributor
timestamp: March 07, 2019, 05:02:33 am
content: Thanks Tim. Much of what you wrote is over my head, but what I did grok gave me some ideas. Unfortunately work is interfering with my play... I'll be back in a day or two.

author: precaud
author_rank: Frequent Contributor
timestamp: March 09, 2019, 04:15:14 am
content: I made a 3:1 version, using a quadfilar twisted bundle. I didn't count turns, but it was a couple less due to the larger diameter of the bundle. It was actually easier to wind, but required two layers. As it should be, stepdown loss was about -10dB.Unfortunately, freq response into 1 and 10 Ohms was little changed compared to the 2:1 version. This is not as it should be.Thinking that perhaps the source impedance needed to be lower to drive it, I tried a buffer amp with 25 Ohm output Z, but no difference.I then looked at the input impedance with the HP 4275A and didn't see anything that would explain the rolloffs. Output Z was about 5 Ohms as it should be.Interwinding capacitance measured 220pF on one set and 330pF on the other.None of this explains the HF response rolloff into 1 Ohm.Is it a property of the core material?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 09, 2019, 07:07:25 am
content: You have about the right impedance for the primary (one strand surrounded by three others is about 50 ohms), but you don't have the right impedance for the secondary (which is 50 ohms again, not 5.5 ohms).Try three twisted pairs, primaries wired in series, secondaries wired in parallel. That gets you closer to having a reference plane's worth of secondary. Probably ideal would be three star quad cables wired up (which is a bit low for the primary (~25 ohms), but about the same amount high for the secondary), but that's more fiddly...Core has essentially nothing to do with the HF cutoff. Incidentally, you don't need to put on so much wire to see what's going on here, as long it's long enough to still capture the HF cutoff in the range of your equipment.Tim

author: precaud
author_rank: Frequent Contributor
timestamp: March 09, 2019, 12:41:36 pm
content: QuoteIt is my understanding that insertion loss scales with the turns ratio (i.e. 3:1 = 9.5dB ), and impedance scales with the turns ratio squared. Yes? So the output Z, with 50 Ohm on the primary, is about right at 5.6 Ohms. And the input Z is pretty close to 9 X (2ndary load R) in the passband.QuoteThat would give 9:1 turns ratio, and 81x Z multiplier!If I'm reading the "reference plane" bit correctly, it suggests that a single layer of interleaved windings is desirable to maintain HF BW. Yes? I could drop down to a smaller wire gauge and achieve that.QuoteYeah, that sort of layup is for machines to do...QuoteThanks for confirming that. I see your point re: # of turns may be excessive. Maybe I'll try removing the second layer and rewiring before junking this and doing one with smaller wire.Thanks fot your input!

author: precaud
author_rank: Frequent Contributor
timestamp: March 09, 2019, 02:24:16 pm
content: BTW, for comparative purposes, would someone who has or has built one of the NVT's show plots of (or measure) the -3dB bandwidth with 50 Ohm source into 1 Ohm and 5 Ohms loads?Picotest specs their J2100A and J2101A injection xfmrs (both 1:1 designs) into 5 Ohms. I inquired of them yesterday about their BW into 1 Ohm, they replied that insertion loss would be greater, low-freq -3dB point would be lower by 1/5th, and high-freq -3dB point would be "substantially the same" as it is into 5 Ohms. Well I don't believe that latter for a second. No 1:1 xfmr I've measured behaved that way. They also offered to measure it if I needed it, which I'll ask them to do, and will post the results.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 09, 2019, 03:31:05 pm
content: Quote from: precaud on March 09, 2019, 02:24:16 pmPrecaud,We can look at the effect of the load resistor on the low frequency -3dB by modelling.I have set the magnetizing inductance of the transformer to be 100mH in this example. The NVT transformers may have higher magnetizing inductance.ModelThe Load is stepped in a 10, 5, 3 sequence from 100 Ohms to 3 Ohms.The amplitude is lower with a lower load resistance, because of the 50 Ohm source impedance.The -3dB point can be found easily when the phase shift is 45 degrees.Modelling ResultsYou can see how the -3dB point is at a lower frequency for lower values of load resistor. But also the amplitude in the flat portion is also reduced.Simplified ModelSince the transformer is 1:1 and the leakage inductance has little effect on the LF response the model can be simplified to:This has the same transfer function as the model above, so the results are not shown.Analytical ResultThe BW can be shown to be:Similar analysis can be done for other turns ratios.Regards,Jay_Diddy_B

author: precaud
author_rank: Frequent Contributor
timestamp: March 09, 2019, 04:11:23 pm
content: Thanks Jay. My modeling software is old (pre-Spice) and on a computer that is down at the moment. I'm more concerned about the HF cutoff than the low-freq one.In that model, L3 is the primary determinant impacting the high-freq cutoff. Where does that come from? How is it determined?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 09, 2019, 05:17:44 pm
content: Quote from: precaud on March 09, 2019, 04:11:23 pmThe leakage inductance, shown as L3 above, and the winding capacitance has an impact on the high frequency response.The leakage inductance is measured by shorting one of the windings and measuring the inductance of the other winding.Model for Leakage InductanceThe magnetizing branch is ignored, because it should not impact the high frequency response.Modelling ResultsWhen I measured HF bandwidth of a common mode choke in this message:https://www.eevblog.com/forum/blog/eevblog-1104-omicron-labs-bode-100-teardown/msg2196759/#msg2196759It did not match the bandwidth predicted by the leakage inductance model, probably because of capacitance.Leakage inductance is minimized by bifilar winding.What is your application that requires you to be concerned about the HF response?Regards,Jay_Diddy_B

author: precaud
author_rank: Frequent Contributor
timestamp: March 09, 2019, 06:20:41 pm
content: OK, I thought it might be the leakage inductance. I'll have a look at that.Somewhere I have a more comprehensive transformer model, one developed and used by Deane Jensen before he passed on. I haven't been able to find it, though.QuoteIt's part of a setup to measure active vreg output impedance using a VNA/FRA. Right now, the setup is good up to 100kHz. At higher freqs, it's all about the distributed bulk capacitance and pcb trace series R and L, which is easier to measure passively. But there's a grey zone, typically in the 100kHz-500kHz region, where sometimes it needs to be powered for accurate results, and sometimes not. I'm trying to extend the bw to enable accurate measurement up into that region, hopefully to 1MHz. The xfmr is the limiting factor.

author: capt bullshot
author_rank: Super Contributor
timestamp: March 09, 2019, 09:03:03 pm
content: Yes, stray inductance matters a lot at low load impedance and MHz frequencies.This is the transformer I mentioned above, made of five wires pulled through a braid shield - the wires in series as the primary and the braid as the secondary. Load impedance is 2 Ohm (five paralleled 10 Ohm resistors).The core is ferrite and doesn't have have as high an AL value as these nanocrystalline toroids, so the low -3dB point is rather high at 200Hz, but the high -3dB is at 4.8MHzThe primary magnetizing inductance is 24mH (@ 10kHz), stray inductance (secondary shorted) is 54uH, and the other way round it's 963uH and 1.28uH.Edit: added the impedance plot (with 2 Ohm load impedance)

author: precaud
author_rank: Frequent Contributor
timestamp: March 09, 2019, 11:12:32 pm
content: Interesting xfmr, capt. Could beveryinteresting with a different core material.Leakage inductance on my 3:1 measures 680nH. XLis 1 Ohm at 240kHz. Which is the -3dB point on the 1 Ohm load curve. So that is indeed the culprit. In order to get -6dB @ 1MHz, Lleakageneeds to be 330nH.Time to start stripping off turns...

author: precaud
author_rank: Frequent Contributor
timestamp: March 10, 2019, 05:58:20 am
content: I peeled off the second layer of turns, leaving 78 primary / 26 secondary. Pri inductance is still a generous 460mH. Leakage inductance is down to 470nH.This resulted in a definite improvement into 1 Ohm: -3dB @ 315kHz, -6dB @ 630kHz. More to come (off) tomorrow.

author: precaud
author_rank: Frequent Contributor
timestamp: March 11, 2019, 01:14:59 am
content: After reading a refresher on the basics of transformer design (maybe should have done that first, eh...), I decided to be cautious and remove 5 more winds. I might have done more, but was concerned that the gaps created between windings would negatively impact core utilization, causing LPriand LSecto plummet.This turned out to be a valid concern. The measured data for the now 63:21 xfmr are:LPri280mHLSec33mHLLeakage395nHCInterwinding132pFSo to get a 15% reduction in leakage inductance, pri and sec inductance went down by 40%. Wow. I can't continue this trend by removing more winds.The resulting transfer response (output / input) is attached. Compared to the 78:26 version, insertion loss was (surprisingly) lower in the passband, and slightly more energy in the rolloff region, resulting in -3dB @ 265kHz, -6dB @ 540kHz. I have no explanation for the better efficiency at low freqs; the impedance profiles look the same as before. I checked all windings with a milliohmmeter and they are all identical.So, while this version drives 1 Ohms with less loss than the last one, the -3dB bandwidth is in fact worse, and I'm no closer to the goal. LLeakwill have to be lower than previously calculated to get the useable bandwidth to 1MHz. Interwinding capacitance at 132pF appears not to be an issue (at 1MHz). Further lowering LLeakis needed. So what's the next step?One idea: by using a larger diameter wire, I could remove a few more winds and at the same time cover the entire core, restoring LPriand LSec. This should lower the CWindingas well.Any other ideas?

author: capt bullshot
author_rank: Super Contributor
timestamp: March 11, 2019, 06:23:47 am
content: Wire resistance would matter for insertion losses, your wire is shorter now - so less losses.Otherwise, while experimenting with transformers, I found the upper frequency being a function of wire length (for twisted pair 1:1 construction).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 11, 2019, 06:46:15 am
content: Quote from: precaud on March 11, 2019, 01:14:59 amFor a given core, winding area doesn't matter -- only number of turns.Magnetizing inductance goes as N^2, while leakage goes as N (for a helical/cylindrical winding shape -- constant wire length per turn), so you get a better deal with more turns. Assuming you can tolerate the higher leakage in the first place, of course.Magnetizing inductance also goes as Ae, so a larger core (cross sectional diameter) also gives proportionally more length/turn, but squared more area, so you get a better deal with more area. Basically, they're equivalent, down to a constant (which will depend on geometry, so your choice of core matters).If you have a hard limit on leakage and therefore turn length, and Zo is already correct, then the only remaining option is to improve the core. If nanocrystalline still isn't adequate.... have you considered some really nice op-amps instead?Note that stacking cores (when applicable -- toroids basically) isn't as good a deal. The turn length goes up faster (compared to getting a bigger core), because the cross section goes rectangular. A low-aspect (square or round) cross section is best.QuoteAmazingly, wire size doesn't matter, it's the relative geometry that matters -- this determines the transmission line impedance.A pair of 0.25mm dia. wires, separated by 0.5mm, hasidenticalimpedance to a pair of 2.5m pipes separated by 5m (heh, assuming they're far enough above ground not to worry about that).You might be using too much length to get away with, say, fine magnet wire, or wirewrap wire, in terms ofinsertion loss-- resistance is independent of TL impedance. But as long as that's adequate, you don't need any larger wire than that.Speaking of magnet wire -- the enamel is quite thin, so if you can tolerate the lower voltage rating, you'll get a much lower impedance, the wires are closer together. Typical twisted pair / bifilar wire is in the 50 ohm range, quite a lot lower than, say, CAT5 pair. That's half the leakage inductance!QuoteHave you tried this yet?:Quote from: T3sl4co1l on March 09, 2019, 07:07:25 amYou noted earlier,Quote from: precaud on March 09, 2019, 12:41:36 pmNo (there aren't even nine wires in that construction!). Just three secondary turns/segments in series, and three primaries in parallel. 3:1 current and 1:3 voltage.Tim

author: precaud
author_rank: Frequent Contributor
timestamp: March 11, 2019, 02:39:29 pm
content: Quote from: T3sl4co1l on March 11, 2019, 06:46:15 amHmmm... I didn't see such a large L loss when removing turns from the 2nd layer. Now that it's down to 1 layer, I assumed it had to do with core coverage. But maybe it was just proportional turns.The other reference says, to lower Lleakage:"Minimize leakage inductance by using a window shape that maximizes winding breadth, and/or by interleaving the windings. And reduce physical separation between windings."The toroid maximizes the shape. But after removing turns and spreading them symmetrically over the core, I've created gaps between the windings.QuoteAt low freqs, true. But not at high freqs, where things like skin effect and proximity matter, yes?QuoteAt this point, winding length isn't that long, 3-4 ft. The 1:1 xfmrs I've been using have much higher Rdc in the windings, so I think I could go with a smaller wire. I have some 26 ga I could try for the next iteration. It would conform to the core closer than the 22 ga bundle does.QuoteYes, I'm already using magnet wire for that reason. Plus, less capacitance and more winds per layer.Quote from: T3sl4co1l on March 09, 2019, 07:07:25 amYeah, my previous understanding of it was in error, I was equating it with parallel impedances. I haven't done it yet, it's more difficult to wind than a single quadfilar bundle. Is there a benefit at high freqs to it? The other source advises against parallel windings: "Paralleling windings or wires within windings succeeds only if the expected division of high frequency current results in the smallest energy transfer."

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 11, 2019, 03:04:14 pm
content: Quote from: precaud on March 11, 2019, 02:39:29 pmThat's just for conventional full layer windups. You've already solved that problem by literally bringing the secondary along with.Try it -- make another twisted pair(s), in free air, connect it up as you would for a 1:3, and measure the high frequency response. You will find the same cutoff; although in this case (no core) you may find the low frequency cutoff is so high it's interfering with this measurement.This is another potentially surprising fact: leakage doesn't depend on core. That should be kind of obvious, actually, since it'sleakingsomewhere -- well, that's what it means, it's not in the windings, and if the windings are on top of each other, it must not be in the core either.It's in the space between windings. (A bank-wound or opposite-limbs winding of course will depend on core, but those also have a lot of leakage to begin with. To put it another way: the windings are so far apart that, the space between them, of course includes some core.)QuoteBut those are loss factors, not reactance factors. Hence, they factor into insertion loss, not characteristic impedance.You're also maximizing performance with a TLT design, in that proximity effect is minimized because the windings are always together.QuoteAgain, that's for whole-layer or multi-layer-per-section conventional builds. The wires are already parallel, and by that I mean the primary and secondary are. Putting more TL segments in parallel only provides more area for image currents to flow, and therefore lower impedance, and therefore lower leakage.I guess there are only so many ways I can describe this. My reasoning is based on EM theory, and proven time and time again in the lab.Tim

author: precaud
author_rank: Frequent Contributor
timestamp: March 11, 2019, 03:51:09 pm
content: Please don't be offended, Tim. I'm just bouncing off of you my limited EM knowledge, and things I've read or seen online. Some of it is apparently BS, or not relevant. For instance, the bit about "core coverage" and "symmetrical placement of the windings" came from a guy on Youtube who was making RF baluns using mulit-filar windings, and said they were important.I'll try your 3x twisted pair and report back. Thanks again for your help!

author: precaud
author_rank: Frequent Contributor
timestamp: March 12, 2019, 03:23:03 am
content: I put together a 3-strand twisted pair version as per Tim's recommendation. I used 26 ga. magnet wire, which is a lot easier to work with than the 22 ga. was. Twisted each pair to about 5 turns/inch and wound one full layer on the core. Here's how it measured:LPri330mHLSec37mHLLeakage235nHCInterwinding290pFCompared to the last windup using 22 ga., LLeakageis nearly halved, and CInterwindingis more than doubled. See the attached plot to see how that plays out in the measured response.Into 1 Ohm, transfer response is -3dB @ 360kHz, and -6dB @ 700kHz. This is the best result yet, by a little bit.Also interesting is that the response into 10 Ohms is better behaved than it is into 50 Ohms. Once it is installed in a proper box with BNC connectors, it appears the HF response should extend cleanly up to 30MHz and beyond with those loads.Tomorrow I'll evaluate the low freq extension and see if I can remove some turns, which would lower LLeakageand CInterwinding.Thanks to Tim for your recommendation. You were spot on!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 12, 2019, 08:45:39 am
content: Bingo.You've got a secondary with characteristic impedance near 10 ohms, hence it performs best matched into that load. Probably it's slightly better still at... 5-7 ohms maybe?Tim

author: precaud
author_rank: Frequent Contributor
timestamp: March 12, 2019, 05:14:28 pm
content: Yes, it would be better at 5.6-ish Ohms, that's the nominal output impedance with 50 Ohms on the primary.The low freq response is flat to 10Hz and -3dB at 1Hz. Without modeling it, I'm leary to start removing turns to reduce LLeakand CWinding. If you go too far, you can't put turns back... So this may be as good as it gets.So how do we reduce LLeakand CWindingfurther? Use a smaller core?

author: precaud
author_rank: Frequent Contributor
timestamp: March 12, 2019, 05:24:15 pm
content: Well this is interesting. Last week I had requested data from Picotest, specifying the response of their J2100A and J2101A 1:1 injection transformers with 50 Ohm source into 1 Ohm load.They just sent me the response plot (S21) for the J2101A. I've attached it. It's quite impressive. -3dB at about 8MHz into 1 Ohm. That's an order of magnitude better than what I'm getting. Hmmm....

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 13, 2019, 12:11:20 am
content: To get leakage lower, keep doing more of it. More pairs in parallel!This reduces Zo overall, however, and with magnet wire, it's probably not a good match to the 50 ohm source anymore.And to do it at 1 ohm, or so on, use a lower ratio, etc.Tim

author: Wolfgang
author_rank: Super Contributor
timestamp: March 13, 2019, 01:28:10 am
content: Dont forget that cable impedance will be the limiting factor.At 10MHz, 1cm of cable with an inductance of 10nH has an impedance of 0,628Ohms, a gross measurement error if you count with 1Ohm.Current injection directly at the point of measurement or a VNA method (series thru) is probably smarter than an extreme injection transformer that cannot be brought close enough to the DUT because its big and bulky.Some ideas:https://electronicprojectsforfun.wordpress.com/power-supply-impedance-measurements-using-the-bode100-lf-vna/https://electronicprojectsforfun.wordpress.com/power-supply-impedance-measurements-for-various-power-supplies/

author: precaud
author_rank: Frequent Contributor
timestamp: March 13, 2019, 03:17:32 am
content: Quote from: Wolfgang on March 13, 2019, 01:28:10 amYes, but:a) the upper-frequency limit of this setup is 1MHz. If I need to look higher than that, I can power the device down and use any number of other tools/techniques, without having to worry about the DC.b) the test leads only extend about 3 inches out from the transformer, andc) the current sense resistor is mounted right on the test clip.All of which is well within the ability of the OSL math to compensate for, well beyond the 1MHz target.QuoteLess bulky than the boxes you have for your Shunt-Thru setup...Also, there are real advantages to xfmr-coupling the signal source when making low-level measurements... the infamous "braid error" problem is eliminated.

author: Wolfgang
author_rank: Super Contributor
timestamp: March 13, 2019, 03:32:40 am
content: Quote from: precaud on March 13, 2019, 03:17:32 amA few *inches* of cable is even long for 1MHz. Anyway, it always depends on the accurracy you want.... The bulky ones are for higher voltage / lower frequency. I have made really small solder-in parts for the fast jobs, but they are not yet on the webpage. Thanks for reminding me

author: precaud
author_rank: Frequent Contributor
timestamp: March 13, 2019, 03:53:51 am
content: Quote from: Wolfgang on March 13, 2019, 03:32:40 amBut I am having no problem with accuracy... if I was, and was unable to solve it, I'd be posting questions about it !I have experimented with Series-Thru (not good for low impedances), Series-R, Shunt-Thru, and Xfmr-V/I methods extensively for quite some time, and for this application (active in-circuit measurement), I prefer the latter overall.QuoteMay I suggest, you might want to make the 'lytics in your boxes nonpolar so you don't have to worry about supply polarity...

author: Wolfgang
author_rank: Super Contributor
timestamp: March 13, 2019, 11:39:45 am
content: Quote from: precaud on March 13, 2019, 03:53:51 amGood point, but I almost never use negative polarities, so I cut corners here. For one app where I needed it I made a special negative only variety. Drawback of unpolarized electrolytics is half the capacitance per volume.

author: precaud
author_rank: Frequent Contributor
timestamp: March 14, 2019, 12:49:21 pm
content: Quote from: Wolfgang on March 13, 2019, 11:39:45 amAlas, I do not have that luxury... almost everything I work on has bipolar supplies.

author: Wolfgang
author_rank: Super Contributor
timestamp: March 14, 2019, 12:55:29 pm
content: What kind of supplies are you working on ?

author: precaud
author_rank: Frequent Contributor
timestamp: March 14, 2019, 01:12:45 pm
content: Varies. But high percentage of linear.Referring back to reply #250. I received confirmation yesterday from Picotest that the plot they sent me of their J2101A xfmr is indeed the mag portion of the transfer function (S21).8MHz bandwidth into 1 Ohm is outrageously good performance for a 1:1 xfmr. It appears that, unlike the Omicron "NVT", this transformer has some real engineering in it. To get that BW, LLeakand CWindingwould have to be an order of magnitude less than what we're getting on these VAC toroids.Anyone care to speculate how they're pulling this off?

author: Wolfgang
author_rank: Super Contributor
timestamp: March 14, 2019, 04:05:08 pm
content: Maybe a split between two transformers, one for HF and one for LF inside

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 14, 2019, 07:33:09 pm
content: Hi,Have you looked at the Picotest J2111A Current Injector?Link:https://www.picotest.com/products_J2111A.htmlIt has a bandwidth of DC to 40 MHz.I am just going to tease with a few photos:These are current waveforms measured with a Tektronix TCP202 probe 50mA/divHere is an application:Measuring the impedance of ceramic capacitor to 40 MHz.Jay_Diddy_B

author: precaud
author_rank: Frequent Contributor
timestamp: March 15, 2019, 01:06:49 am
content: Very cool. But way overkill for my needs. And pricey to boot...

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: March 15, 2019, 01:11:05 am
content: The pictures I posted are from myDIY versionnot the $1500.00 Picotest boxJay_Diddy_B

author: precaud
author_rank: Frequent Contributor
timestamp: March 15, 2019, 01:51:43 am
content: You don't really need the extra current to resolve the minima on those caps, do you?I've been surprised by the number of times I've had to dial back the drive current to get a good Z reading when testing regulators on-board. Especially 78Lxx's in circuits pulling only a few mA from 'em. The drive current can modulate the output impedance!

author: precaud
author_rank: Frequent Contributor
timestamp: March 19, 2019, 01:02:31 pm
content: Another data point regarding using these transformers into 1 Ohm loads. This shows the level response of various transformers, with 1VRMS input from 50 Ohms source. The good news is, any of them are able to drive 1 Ohm relatively flat from 10Hz to 1MHz with a useful amount of current for the measurement. So other criteria will (or can) determine which one to use.Would still be interested if someone who made an "NVT" would post its S21 into 1 Ohm, for comparison.

author: precaud
author_rank: Frequent Contributor
timestamp: March 20, 2019, 02:16:27 pm
content: Another interesting aspect of this is: the interaction between the transformer's nonlinear response vs load and freq, and the workings of the Open-Short-Load math.In a nutshell, the OSL math works by assigning, at each measured frequency point, real & imag values that define the short and open conditions, plus one "known" impedance value. All measured impedances are then mapped or scaled linearly to those values.For this to work, the transformer has to have a transfer response that is linear with load and frequency within the ranges you're wanting to use it. This is a tall order into low Z loads.I decided to evaluate some xfmrs over my desired range of use: from 0 to 10 Ohms, and 10Hz to 1MHz. Other than xfmr saturation, there were no linearity problems at low freqs, so I evaluated them at four freqs (10kHz, 100kHz, 500kHz, and 1MHz) and seven resistances from 1 Ohm to 10 Ohms. (With a 1 Ohm current sense R, this corresponds to a measurement range from 0 to 9 Ohms). I converted the S21 to real/imag values and plotted them on a linear scale. This will give immediate visual indication of what is the best OSL "Load" resistor to use with that xfmr, and over what impedance and freq ranges the xfmr can be used with OSL compensation to give accurate results.Since Tim's 3:1 xfmr with paralleled secondary gave the best HF performance, it was first. The plots shows S21 at the 4 freqs and 7 impedances for each, with a line from the 1 Ohm point to one of the upper-impedance points to highlight the linearity of the data points.The first plot shows the 3:1 with linearity to 10 Ohms. Up to 100kHz, it is excellent. So used with a 9 Ohm Load R, this xfmr would deliver accurate results from 0 to 9 Ohms up to 100kHz.But at 500kHz and 1MHz the OSL math would not correct the measurement accurately. The measured points are highly nonlinear. The 2nd plot shows that its linear range at high freqs is only to 2 Ohms. So this xfmr would give good results up to 1MHz with a 1 Ohm Load R measuring 0 to 1 Ohms, with increasing error at higher Z's.This is a much narrower operating range than expected or hoped. It wipes out any advantage gained by the unit's better HF response.

author: precaud
author_rank: Frequent Contributor
timestamp: March 20, 2019, 02:36:24 pm
content: Let's look at the xfmr that HP used to recommend for this test setup. A North Hills 0017CC 1:1 50 Ohm xfmr.It's linearity to 10 Ohms is much better than than the home-rolled one. Not excellent, but probably good enough; at least the vector is pointing in the right directionGreatest error would be between 100k and 500k Hz. But it is indeed useable over that Z range to 1MHz.Drop the Z range and reference Load R to 4.7 Ohms and its better. And you can see that at 3.3 Ohms, it would be quite good.

author: precaud
author_rank: Frequent Contributor
timestamp: March 20, 2019, 02:51:35 pm
content: And here's one that is even better yet. A North Hills 1111LA 1:1 75 Ohm xfmr. Who woulda thunk that a 75 Ohm xfmr would give better results at low Z's. (There are two versions of the 1111 currently being offered on eBay, either one would work fine. I have no affiliation with the sellers.)https://www.ebay.com/itm/North-Hills-Wideband-TRANSFORMER-75-Ohm-20-HZ-NOS-w-Box-r6/302863195770https://www.ebay.com/itm/North-Hills-1111LB-20Hz-6MHz-Wideband-Transformer-NEW/254149491185?epid=12021216572The 1111's data linearity is better that the 0017 at 10 Ohms and 4.7 Ohms up to 1MHz. With 3.3 Ohms (the next dot down), it is about as good as you can expect to get from any xfmr.Comparing these three xfmrs, what appears to make the difference is how gradual the S21 HF rolloff is. Higher-Q responses that maximize the flatness but cut off faster aren't as useful as a well-damped rolloff.

author: BFX
author_rank: Frequent Contributor
timestamp: November 03, 2019, 06:04:03 pm
content: I did some research and here is the resultAny similarities is only by chance:D

author: Wolfgang
author_rank: Super Contributor
timestamp: November 03, 2019, 07:24:55 pm
content: Quote from: BFX on November 03, 2019, 06:04:03 pm...looks too close to the original and has no nude virgins. Something for married people.

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: November 28, 2019, 07:57:55 pm
content: Quote from: Jay_Diddy_B on March 15, 2019, 01:11:05 amDo you have a post for your DIY injector?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 29, 2019, 07:32:02 pm
content: Quote from: sixtimesseven on November 28, 2019, 07:57:55 pmNoAt least not at the moment …Regards,Jay_Diddy_B

author: ch_scr
author_rank: Frequent Contributor
timestamp: February 13, 2020, 04:17:02 pm
content: We have tested a different option and found that two huge chinese MnZn cores (search for "Cores Green 75mm x 39mm x 13mm") stacked on top of each other and afterwards wound in a similar fashion (not in the number of turns, but in terms of covering the core with windings, style of twisted wire and connection) to the Bode 100 transformer gives the attatched result. Seems like a lot of wideband transformer for about 10€ for the cores. The much increased volume of core material might also help with saturation?

author: David
author_rank: Frequent Contributor
timestamp: March 23, 2020, 09:54:02 pm
content: Apologies to break up the discussion on the injection transformer for a moment but could someone explain in a little more detail the architecture of the bode 100? Is this essentially a superhet performing a sweep of the frequencies via sweeping the LO to maintain the IF which is fed to the ADC? Is this the same technique used in FFT analysers? (E.g. the Stanford SR series). I didn't see a mixer or LO (assuming one of the DDS?) In the teardown?Cheers,Dave

author: sorin
author_rank: Frequent Contributor
timestamp: April 20, 2020, 12:21:46 pm
content: Quote from: ch_scr on February 13, 2020, 04:17:02 pmPlease can you post a photo of your final product

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 21, 2020, 02:29:05 pm
content: Quote from: ch_scr on February 13, 2020, 04:17:02 pmHi,Can you post a schematic showing how this transformer was measured?If I calculate the inductance:for one core:Area = Thickness x (D - d)/2WhereD= outside diameter = 75mmd= inside diameter = 39mmThickness = 13mmArea = 13 x (75-39) /2 = 234E-6 m2Mean magnetic Path lengthPi x (D + d)/2 = PI x (75 +39) /2 = 180E-3Assume that this core is a power grade of ferrite with a relative permeability of 2000.AL= mu0x murx Area/lengthAL = 4E-7 x Pi x 2000 x 234E-6 / 180E-3= 3.28uH per turn2Assume 50 turnsLmag = 502x 3.3uH= 8mHand two cores stacked would be 16mH50 Ohm test circuitThe LF -3dB for this configuration is calculatedR1 // R2 = RLF(-3db) = 1/(2 x Pi x L/R)= 250 HzIt just seems too good …Regards,Jay_Diddy_B

author: jmw
author_rank: Frequent Contributor
timestamp: April 28, 2020, 04:23:58 am
content: I bought a VAC T60006-L2040-W424 and used a 23AWG pair from a plenum CAT6 cable. For the life of me, I could not get more than 29 turns on the core. Maybe the original uses 24AWG or something smaller?I don't have a two-port VNA but I used the Bode function on my scope (with a 50 ohm feed-thru term on the sec. side). Flat and phase response below 5 deg until just below 1 MHz, good enough for my needs.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 28, 2020, 12:36:26 pm
content: Hi,I suspect that you are not measuring the transformer correctly.To test the transformer in a 50environment you need to use the top circuit here:I suspect that you are using the bottom one. In this configuration you should read -6dB in the flat portion.If you use the bottom one you don't see the impact of the magnetizing inductance.Regards,Jay_Diddy_B

author: jmw
author_rank: Frequent Contributor
timestamp: April 28, 2020, 09:33:25 pm
content: Hi Jay_Diddy_B, I repeated the test to your procedure:So it seems by 3 dB points it is good from 40 Hz - 2 MHz, and by 5° phase limit from 500 Hz - 200 kHz. Not spectacular by others' work, but still adequate for evaluating the feedback look on many switchers. I'm still puzzled on the turns count and why I'm topping out at 29 if people got 40 using 23 AWG... but my expectation is that more turns would help at the low frequency and not so much the high end.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 28, 2020, 10:07:38 pm
content: Quote from: jmw on April 28, 2020, 09:33:25 pmHi,40Hz means that the magnetizing inductance is about 100mH.I am not sure that other people measured them correctly.It is very useable.Regards,Jay_Diddy_B

author: Roland_W
author_rank: Contributor
timestamp: July 01, 2020, 12:48:31 pm
content: Hi, All,I read the all about the Injection Transformer.I need one, and as Wolfgang I build one using the same core VAC T60006-L2030-W514 :https://pl.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2030-W514?qs=ePbE9GiMmvVKrWoTvqBaIQ==I use a RJ45 cable twisted pair 10 m long.I wind first layer and I measure using the Diligent Waveforms Analog Discovery 2 to measure frequency response.I make first measurement when I done the first layer of the winding – orange one, second layer winding – blue one, and the third – yellow one.More turns move lower the working frequency.

author: MilkmanCDN
author_rank: Contributor
timestamp: August 06, 2020, 01:37:09 am
content: Quote from: jmw on April 28, 2020, 04:23:58 amHey there. Are you sure you bought the L2040? There are a few posts on this thread stating that the L2030 is the transformer used in the BWIT-100. I first purchased the L2030 and had the same problem as you (I could only get about 29-30 turns around the thing). It was then that I realized that the L2040 is a larger core and in fact the one used in the BWIT-100, which will accommodate the required 40 turns.See reply #216 in the thread for details. I've since purchased a used Bode100 and verified performance of the transformer (which is identical to the original).

author: jmw
author_rank: Frequent Contributor
timestamp: August 06, 2020, 01:56:02 am
content: I bought it from Mouser, and part # from the order history checks out, but there is the small chance they did a bad pick. I'll make a note to check the dimensions on it tomorrow at the lab, and the datasheet for T60006-L2040-W424 says it is 40 mm OD / 25 mm ID.Edit: dimensions match the L2040 datasheet...

author: CChin254
author_rank: Regular Contributor
timestamp: August 07, 2020, 03:55:57 am
content: I did an IC Identification of this device. The back SOT-23 packages are probably all ON Semiconductor MDC3105LT1 Integrated Relay, Inductive Load Drivers.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 07, 2020, 09:45:36 pm
content: Quote from: Roland_W on July 01, 2020, 12:48:31 pmHi, looks interesting but for my taste the windings on top of each other create some wiggles at the top end due to interwinding capacitive coupling.Anyway, its flat enough for many purposes.

author: _Wim_
author_rank: Super Contributor
timestamp: August 08, 2020, 06:16:38 am
content: Quote from: CChin254 on August 07, 2020, 03:55:57 amNice job and interesting to see. Thanks!

author: TimNJ
author_rank: Super Contributor
timestamp: October 23, 2020, 10:37:50 pm
content: For anyone who has DIY'd one of these injection transformers, what have you used to actually plot the gain/phase of the power supply under test? Some sort of low frequency network analyzer sounds good, but if you don't have one...what are some reasonable options? Are you better off doing it manually with a sine wave generator and oscilloscope?From watching one of Keysight's demo videos , seems like he had to a do a fair bit of fiddling to get accurate measurements since an SMPS can be quite noisy, and you have to separate the uncorrelated noise from the measurement. Seems like the dedicated software probably has some decent DSP to extract only the real signal.Measuring manually lets you make the decision on what's noise and what is not. But, also will probably take a while if you're going to cover 4 or 5 decades.Any ideas?

author: Wolfgang
author_rank: Super Contributor
timestamp: October 24, 2020, 02:14:04 am
content: Hi,I measured my stuff on a Bode100 and on a Keysight E5061C-3L5.Bode100 is pricewise OK, E601C-3L5 is extremely expensive.Whats different when measuring on a scope:- dynamic range is a lot less due to scope resolution (cheap ones have 8 Bits only)- no small bandwidth as on a VNA that filters out spurs- FFTs a bit kludgy (except when scope is expensive)What can you do:- Get (if you can) your scope into some high-res mode- Hook up your injection transformer to a signal generator- Use a PC to step the signal generator and get scope traces per step into you PC.- Make steps small enough so you dont miss a peak. Step logarithmically.- do a manual FFT using Python in the PC. No strong harmonics of the injected signals should be there, otherwise its too strong.- Map gain and phase for each step- If you find suspicous peaks with gain close to one, those are the weak spots to work on.Alternative:- Connect a load pulser (fast enough for your PSU) and inject a step load current pulse- Observe pulse response for ringing. Reverse transform gives transfer function.Another idea:- Use a flat noise source (could be an ARB)- Amplify it- Drive a current injector with it (watch for linearity !)- Measure output voltage without and with noise on- FFT and average the result. Voilá, here are your peaks.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 24, 2020, 03:52:27 am
content: Hi,I use an old HP 3577A.This is a 5 Hz to 200 MHz VNA.It has 10Hz filters it is very good for measuring SMPS control loops.Regards,Jay_Diddy_B

author: TimNJ
author_rank: Super Contributor
timestamp: October 24, 2020, 04:52:19 am
content: Thank you all.For most of the projects I've worked on, checking stability with a dynamic electric load has worked well. With current mode control, and some other newer control methods (for example, TI's "hybrid hysteretic control"), reaching stability seems pretty trivial these days. I am still curious roughly the gain margin of these converters, from an educational perspective.The semi-automated PC method seems reasonable, but do not have a PC compatible function generator. (Could purchase the AWG package for my scope and use it remote.)I wonder how Analog Discovery 2 would fare in this application. It has a 14-bit DAC, so I suppose that's a plus for measuring low amplitude signals.https://reference.digilentinc.com/reference/instrumentation/guides/waveforms-network-analyzerI downloaded the Waveforms application, and checked out the network analyzer function. It looks okay, but am not sure what the measurement RBW is for the network analyzer. Or, in general, I don't know how it would handle being blasted by switching noise/ripple.

author: jmw
author_rank: Frequent Contributor
timestamp: October 28, 2020, 03:30:05 am
content: The Keysight 1000-X has a frequency response analysis program, and I think it's an option on other scopes. The dynamic range is pretty terrible, if one channel is more than 30 dB than the other, then the plot gets really noisy. It's still good for looking at the crossover region.This is Bode chart I made for a flyback converter, using my homebrew injection transformer. Prior to the test, I picked the compensation components to get a crossover at 12 kHz with a 60° phase margin based on an analytical model of the feedback loop.

author: TimNJ
author_rank: Super Contributor
timestamp: October 28, 2020, 04:04:04 pm
content: Quote from: jmw on October 28, 2020, 03:30:05 amInteresting. Thanks. I was not particularly impressed by the amount of human effort required to get a reasonable measurement, in the Keysight video. I do not yet have a DIY injection transformer...I will try JDB's EPCOS common-mode choke transformer suggestion + an oscilloscope in hi-res or averaging mode. I wonder how long it would take to "manually" record 5 decades of information with 10 samples per decade. Probably about 45 minutes if you're dedicated? Not great, but maybe okay if you only are doing it occaisionally.

author: Alextsu
author_rank: Contributor
timestamp: October 31, 2020, 05:41:57 am
content: Hi, Tim,You're looking in the right direction.Yes, AD 2 will do the job. The amount of noise filtering depends on the integration settings.I had used a black legacy AD to measure frequency responses of several AC-DC PSU.I had also compared it's performance against other test instruments.The only issue You may run into with AD is a poor USB PC connection noise immunity.Quote from: TimNJ on October 24, 2020, 04:52:19 am

author: TimNJ
author_rank: Super Contributor
timestamp: November 02, 2020, 05:06:17 pm
content: Quote from: Alextsu on October 31, 2020, 05:41:57 amThanks very much. Do you think a USB isolator + separate USB battery pack would be a useful approach? As I am not familiar with the Waveforms software, where are the integration settings located? I could not find much adjustment in the GUI menus.

author: Alextsu
author_rank: Contributor
timestamp: November 09, 2020, 02:24:32 pm
content: Quote from: TimNJ on November 02, 2020, 05:06:17 pm

author: jmw
author_rank: Frequent Contributor
timestamp: February 01, 2021, 06:39:37 pm
content: I got some time in the shop to drill enclosures for mine and a few of my other odd test tools. No nude virgins, but I'm calling this look "midcentury space-race brutalism"

author: Wolfgang
author_rank: Super Contributor
timestamp: February 01, 2021, 11:12:49 pm
content: The proper term is early Hammond Era "Art Brut". My preferred building style.How did you get the letters on the boxes? I used an oversupply of overhead foils and a laser printer ...

author: jmw
author_rank: Frequent Contributor
timestamp: February 02, 2021, 02:19:35 am
content: There's a huge 120 W CO2 laser here, so I used a laser marking spray (https://enduramark.com/- there are several others sold under CerMark, LaserBond). The results have been pretty nice and durable.

author: RamboChen
author_rank: Newbie
timestamp: July 12, 2023, 06:14:06 am
content: Hi, Thanks for your good job!is there have any more detil information about the receiver channel(or some Clear images)? i‘m try to analysis it's mixer principle.

author: miro123
author_rank: Frequent Contributor
timestamp: March 30, 2025, 09:39:46 am
content: Another theardown of Bode 100 TH test fixture

author: miro123
author_rank: Frequent Contributor
timestamp: March 30, 2025, 09:46:49 am
content: Then the question. How does this circuit works? Is it kind of direction coupler or LISN?The answer of those questions can shed some light about the principle of working of this equipment.

author: shabaz
author_rank: Frequent Contributor
timestamp: March 30, 2025, 10:11:38 am
content: It simply uses that test fixture box to obtain the amplitude and phase difference compared with the stimulus signal (stimulus is measured from channel 1, and the DUT is measured with channel 2. The resistors are used to form potential dividers.You can't obtain much more about the implementation of the test equipment from just the test fixture box. But I imagine it internally may well contain a DSP chip or microcontroller to generate the stimulus (i.e. with a DAC), and use two ADCs to perform the measurements. From the amplitude and phase difference, it will be able to perform the calculation (and then repeat at the next frequency). At least, that's one possible implementation. I know nothing about that particular test instrument.EDIT: Looking at the product page, it mentions there are superhet receivers internally. So, it's likely that the two channels (stimulus and DUT) are mixed down to either a very low frequency, or perhaps to DC, and then a couple of high-res ADCs) e.g. 24-bit can be used to perform the measurements.

author: precaud
author_rank: Frequent Contributor
timestamp: March 30, 2025, 12:08:20 pm
content: Your question has already been answered:https://www.eevblog.com/forum/testgear/mini-teardown-omicron-b-wic-impedance-test-adapter/?nowap

author: shabaz
author_rank: Frequent Contributor
timestamp: March 30, 2025, 11:46:11 pm
content: You can better understand it by re-drawing the diagram to see the two potential dividers.(Note: since I don't have access to the test fixture, the attached schematic may still have errors; if there are any, let me know, and I'll fix the diagram).From the video, you can see how it approximately works; a stimulus is generated with a DDS, possibly switched in amplitude inside its metal can, and then that is received on the Source input on the test fixture, where it is applied to both potential dividers. The outputs from the potential dividers are the reference and DUT signals, and they will have an amplitude and phase difference depending on the DUT impedance.Next, both of these signals are independently mixed (there are a lot of switches inside the metal cans to presumably do that!) with a second DDS-generated signal, which will have a precise relationship to the stimulus signal. That precise relationship will very likely be at least zero degrees and perhaps 90 degrees (alternated possibly) if mixed to DC. Your output signals from the mixer will then simply be digitized (there are two 24-bit ADCs, one per channel), and then all the data is sent into the PC (there may be some digital signal processing on the PCB too).