binding post to BNC impedance analyzer test fixture? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 12:33:12 am
content: So if you have a impedance analyzer and you can connect a BNC to banana binding post adapter to the measurement point, what frequency is this useful for?I calibrated the impedance analyzer using a BNC short, BNC open (dust cover) and BNC 50 ohm load. When I attached the dual binding post to it, it read a capacitance of 4pF roughly when open circuit. When I added a 2pF capacitor to it, it read 6pF.So I can easily stick a piece of braid as a short circuit (or maybe a cutout of copper sheet that conforms nicely around the binding posts like a shorting jumper on old HP equipment), leave it open for open circuit, then put say a 1/8 watt leaded resistor between the posts to get a '50 ohm' calibration. I have not tried this yet.But anyway, any conjecture on when this stops being accurate (or gets highly inaccurate)? I measured a 330pF 1% capacitor on it and it measured correctly. I am using a old HP BNC to binding post/banana adapter. I wanted to know the theory of what starts going wrong as you increase frequency with this setup.. (its for a 4191A impedance analyzer with bandwidth of 1MHz to 1GHz). I also cross tested the APC-7 cal kit with the crappy BNC 50 ohm load and it seems to be within a few percent, and I am using a direct APC-7 to BNC adapter. It seems like a good enough idea for leaded parts...I wanted to know if there is some kind of debilitating problem before I try ordering some precision through hole components that maybe have some frequency data to test on it (might save me a few dollars to post this).

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 27, 2022, 02:40:03 pm
content: I don't know what sort of fixture or connector you are using, Are you using a APC to BNC or do you have the HP fixture?They had several fixtures for the 4191 A, but also the manual states that the APC7 could be used for a user built test fixture.There was even a "probe"Their "spring clip" adapter advertised good to 500 MHz not 1 GHz Binding post adapter good to 250 MHz More practical HP binding post adapter good to 125 MHz See page 3-34 and 3-35 in Manual.I suppose you have it but here it is anyway (maybe for the ease of others reading this)https://www.keysight.com/us/en/assets/9018-05401/user-manuals/9018-05401.pdf?success=trueI suppose you could make a decent test fixture that accepts Banana and calibrate out most of the error. Probably much less than 100 MHz.Maybe you could make a binding post design that would work at 100 MHz reasonably. Theirs uses a "guard"Just guessing about the 100 MHz.BNC open short load stuff is all over the map and some are not very good. I have a bunch of brand name 50 ohm loads that are not good to 100 MHz.If you find a reasonable good source for high quality "standards" for caps and inductors and resistors, let me know,Wally

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 03:58:44 pm
content: Well I notice that those fixtures attempt to reduce inductance as much as possible (loop area?)is this because there is complex coupling between the DUT and the fixture that you can't calibrate out easily since a fixture with a higher inductance has a higher loop area/more radiation/coupling (since its starting to be treated as distributed analysis)? (i.e. you do a 50 ohm calibration but when you stick a 500 ohm resistor in there the turns count on the coil is so high it starts working with the fixture to do complex/nonlinear things so the results are useless because the part interacts with a test fixture in a way that is not calibrated?)its mad annoying that those parts are mad $ for something that looks like some plates lol, I wanted to know why I need to invest so much. You would at first glance think you can calibrate everything out. I am scared of the news groups because those people are like primal engineers with venom sacks still attached (TNG: Genesis, S07E19), it looks like a rough placebut this machine does look like it fell off the enterprise

author: joeqsmith
author_rank: Super Contributor
timestamp: August 27, 2022, 05:33:54 pm
content: Some time ago I used the NanoVNA ($50) to attempt to analyze a power distribution network. During part of the demonstration, I used a breadboard and plugged in some components to form a simple RLC network. I left the long leads on the parts and ran a sweep to 50MHz. I then repeated the test with the component leads cut short.It's not exactly what you are asking but it may provide you some idea of what to expect.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 27, 2022, 05:41:05 pm
content: I only know enough to be dangerous.I think the test fixtures are designed with the same sort of idea in mind as designing COAX. in that the impedance is constant over a big freq range.I know there are fixtures for the four connector LCR meter fixtures available from Tonghui and I have one that works fine at 1 MHz. It does not look that complicated to make one and they did it for far less than the used HP ones are going for. I do not know any sources for other test fixtures for APC connectors.At the prices they have on e pay for the HP APC fixtures, I think you could get a machine shop to make a few...if you had the APC of course. Or design a board and get some boards made and have nice connectors made from solid silver, it would seem to be cheaper.I wonder if anyone has just replaced the APC with a different system, I do not know. Apparently all the connections are made to the one APC connector internally, making the stray impedances less but making connection more critical, I guess...

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 05:59:44 pm
content: BTW I highly recommend making racks because then all those 'pains' that people complain about with older equipment go away. All you need is a cable storage bin to make any connection that you want. It might save you money in the long run. Good wheels too to make it easy to move around.I was able to do a similar experiment with my banana adapter. You take the capacitor with long leads and let it stick out of the binding post adapter, take a measurement, and then you stick it in so the capacitor is closer to the binding post with the leads hanging out the other end. The resonance point does move around.I think I will order a few cheap but good parts and perform measurements that have the part soldered in a connector like a terminator and compare it to the part in the banana adapter. Actually I might have a eBay leaded inductor kit that I got a decade ago that had some parts that IIRC had quite a high operating frequency range in the VLF band to test this, I think I was waiting for more then a decade to find a use for that lolhttps://en.maritex.com.pl/product/attachment/90429/749fb5a97de04985f84d9d6a0b8a1e80*SRF of inductor is either 180Mhz or 200Mhz minimum, I don't have the part label but I think its the 0.9uH from the datasheet, the damn label on the paper got lost

author: joeqsmith
author_rank: Super Contributor
timestamp: August 27, 2022, 06:20:43 pm
content: I had forgotten that I also show the same circuit built up on a PCB with surface mounted parts which further improved the performance (shocking!!).You could maybe make up a custom fixture easy enough but no harm just starting out with the BNC to banana adapters. For what you are trying to do, these may prove good enough.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 06:35:46 pm
content: Well I put a strip of copper sheet in there for a short, left it open as a open and put a 51 ohm metal film resistor as a load, in order to do the calibration in the adapter rather then with the BNC standards that made the fixture read 4 pF.Now the fixture reads 0.06pF after calibration, and the difference is1) calibrated with BNC short, BNC dust cover and cheap 50Ohm BNC load that seems to agree with a APC-7 cal kit BNC load OKish.inductor reads ~880nH at 1MHz, and 1205nH at 55 MHz2) calibrated with copper strip, resistor and nothinginductor reads 885nH at 1MHz and 905nH at 55MHz.So the difference between the two calibrations (one that 'compensates' for the fixture is a difference of 425nH and 20nH with a difference of 54MHz. The inductor claims to have a min SRF @ ~200MHz. Defiantly a big difference, but there is still too many unknowns since the calibration resistor is just a random cheap 1/4 inch metal film with the thin leads lol, but it certainly looks more linear given the high SRF of the inductor.so 2% change vs 31% change with same parts. If that inductor is really as stable as they say with a high SRF, I am inclined to trust the crappy calibration then the coaxial calibration?What would be a nice through hole resistor to attempt to play with this fixture more that has good RF parameters.. it needs to be 50Ohm. I would prefer a leaded part and not to solder leads to a SMD part (i hate this). I also need to measure out a thicker copper sheet to act as a shorting standard because I used like copper foil and it was pretty dodgily cut (it reads like 20-30miliohms after cal when you put it back in, the shorting BNC (amphenol) reads approx 15-20 miliohms) at 1MHz.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 06:58:33 pm
content: Unless there happens to be a long RF SMD resistor that fits between the binding posts naturally (so like a 1/2 inch long 50 ohm resistor that is SMD would be acceptable, since thats not that different from the metal plate, if a wired one is not good enough.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 09:17:45 pm
content: It looks like the SRF is 304.5MHz (from ind to cap), the inductor must have been a 5% 1uH inductor with a datasheet minimum SRF of 200MHz. The De5000 shows 1.0uH @ 1KHz

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2022, 09:37:01 pm
content: Quote from: coppercone2 on August 27, 2022, 06:58:33 pmIn the 1990s, I used an -hp- 8753A network analyzer (with reflection bridge) or an -hp- 4191A impedance analyzer (both of which had APC7 connectors at the test port) at frequencies below 100 MHz.Specifically, I needed to measure balanced impedances substantially above 50 ohms; the following system worked well.We made test fixtures for different ranges, using inexpensive MCL transformers (in flattened-DIP packages) appropriate to the frequency range, terminated in a female connector with 0.200" spacing that matched the MCL package.The mating connector was a standard 0.200" male header (with the center pin of three 0.100" spaced pins removed).We calibrated the system with simple male headers: either open (nothing connected), short (copper foil between pins), or the appropriate resistor (1206 SMT) at the higher resistance.Below 10 MHz, we went as high as 13 k, the design value of one MCL transformer. The 8753A firmware allowed us to set the characteristic impedance, but we had to cheat and tell it we calibrated to 130 ohms, due to firmware limit.I don't remember if we soldered the 50 ohm end of the transformer to an N or BNC connector, which connected through an APC7 adapter.Since the connector and adapter were before the reference plane (0.200" male), the errors were taken out by calibration.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 09:52:40 pm
content: I think I Happen to have some chokes/transformer in DIP package (for network cards), IIRC the frequency range was in the area /past the area you are saying. Measuring balanced impedances as actually my next target BTW

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 10:03:54 pm
content: What do you recommend I measure with a balanced impedance that I could know the system is working properly? Are there any standard objects that might be in the lab that fit the bill? A piece of network cable or something?

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 10:26:09 pm
content: Also, what BNC did you solder the transformer to? I assume it has to be a PCB BNC right. A BNCM PCB mount that goes to the mcl that goes to the dip f? I don't think you had a BNCm to pc7, their usually BNCF...? I don't think you used the chassis mount versions right... the body is too hard to solder to without effecting the seals. This sounds like kind of funAnd I gotta say it sounds maybe tempting to try this with a twinax instead of headers too.

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2022, 10:31:02 pm
content: I would try a series of 1206 resistors, of measured resistance, which should be reasonably non-reactive.When measuring self-resonant frequency of capacitors, I found that one could assume an equivalent series inductance that depended only on the total length of the "capacitor" in circuit. Specifically, with roughly 0.75" total length, a set of capacitors between 1 nF and 470 nF had approximately 10 to 15 nH ESL, regardless of capacitor type (disc ceramic, multilayer ceramic, or even polystyrene foil).(These measurements were all made at roughly 10 MHz for a specific project.)

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2022, 10:32:06 pm
content: Quote from: coppercone2 on August 27, 2022, 10:26:09 pmIt's been a long time, but I believe we soldered the primary leads to a chassis N female connector, then used appropriate adaptors to the APC7. These are all before the reference plane, and calibrated out.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 10:36:03 pm
content: How do you solder the body of the N? That is so big, it makes me want to use a blow torch. Whenever I solder the body of a BNC (let alone a N) the dielectric seems to over heat, and BNC have their rubber gasket expand and make them tough to connect.PC mount has little studs that you can easily solder to that come out (I guess its a bit of extra inductance). I made like 5 or 6 different things soldering BNC connector bodies, and I would say 5/6 have toasted dielectric. So for low frequencies I switched to 75ohm board mount BNC, the dielectric is teflon so its harder to over heat and you can easily solder to the legs of the connector that are supposed to go to the PC board (this is the easy way to add a pipe to a connector with out a forming tap, if you don't mind a small gap in the shield). Maybe if you spot weld a brass*tube segment (thin) to the N body so it has a elevated ring you can solder that easily...

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2022, 10:50:08 pm
content: There are insulated BNC panel females with 2 solder cups side by side.https://www.digikey.com/en/products/detail/amphenol-rf/031-10-RFXG1/2643384?utm_adgroup=Coaxial%20Connectors%20%28RF%29&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Connectors%2C%20Interconnects&utm_term=&utm_content=Coaxial%20Connectors%20%28RF%29&gclid=EAIaIQobChMI_O6OgpDo-QIVnwqtBh005Q4bEAQYASABEgKzYPD_BwEA 4-mounting-hole panel N female can take a small solder lug (4-40 screw size) at one of the mounting holes.A normal soldering iron works with the flattened DIP leads of the transformer into the solder cups or lug.I'm referring to panel connectors (with female center connection), not cable connectors.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 11:18:06 pm
content: ah ok you put a solder post there, that could work nicely. Or you can solder a post to a screw and then thread the hole if you want also.I have some of the isolated BNC connectors but if you look how they are built, the area where you solder to looks like it has more inductance, the one I have here right now looks like there is a metal shim going down a few MM in to the body, where the chassis mount one its a coaxial right up to the level of the dielectric, so theoretically you can shorter the center pin and if you can solder to the body its going to be lower inductance. I guess it does not really matter too much, and manufacturability and durability is more important.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 11:21:08 pm
content: Actually I have a bunch of old waveguide to 3.5mm adapters I found in the trash (like 30 of them) a decade ago. The distance between the center pin and screw hole of the 4x flange is almost perfect for a DIP chip. I wonder if I can hammer a copper wire into the hole like a rivet to make a 'surface mount' solder point for the transformer.

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2022, 11:27:16 pm
content: Quote from: coppercone2 on August 27, 2022, 11:18:06 pmAgain, if you apply the open/short/load standardsafterthe transformer secondary, a reasonable amount of stray/unintended impedancebeforethe primary will be removed by the calibration. I am just telling you what worked for my application 20-30 years ago as a suggestion.

author: coppercone2
author_rank: Super Contributor
timestamp: August 27, 2022, 11:34:40 pm
content: well I guess that might start to answer the main question of this thread, which is how much can you cancel before something bad happens. It seems to be at least the amount of a isolated BNC connector and header pins inductance for under 100MHz.

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2022, 11:39:58 pm
content: Using a reflection bridge method (4191 or 8753) will give you the impedanceat the plane where you placed the standards. The BNC isbeforethat plane, extra leads can be after that plane.To check the method, I suggest trying two 1206 resistors, one 3x lower and one 3x higher than the “load” resistor used in calibration.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 12:33:51 am
content: well I wonder what would happen if you put a meter of romex before the calibration plane. What I am asking is how bad can it get before the calibration does not work (assuming you have enough power for the measurement to over come pure attenuation). Like is HP making those crazy test fixture just to run the output amplifier by a few dBm lower.. or is there a nonlinear error of some kind that manifests itself when it gets bad. Like I could imagine it working after a very long piece of coax, but what if its downright improper. Is interference all you need to worry about, or is there self interference between the DUT and the test fixture based on the properties of the DUT that are different then the load (i.e. like coils).

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 03:08:04 am
content: HP has described the process in their manuals and app notes. If there’s too much crap before the reference plane, the error can be too large for the calibration process to yield an accurate correction.As I remember from the 4191A manual, if you needed to extend the plane far from the APC7 connector through a length of real coax, not Romex, they have a couple of SMA (actually APC3.5) connectors where you should add a corresponding length of 50 ohm transmission line. This is all quantitative, not handwaving.Mathematically, this is a “linear” problem, but subtracting large numbers from each other may not give an accurate result.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 03:13:16 am
content: Are you sure its entirely linear? Like imagine if part of the fixture is an antenna and there is say a inductor focusing a field on it. I can't visualize the feedback loop that well, I don't have enough experience, but like a perfect calibration resistor can't be the same as a rod inductor with two big poles right? I think you would need some kind of model... or am I missing something? I guess its all near field.Or like a loading coil. Won't some specific impedance turn something in the test fixture structure into a efficient radiator (to some degree)? Is it correct to think this happens (even if under a reasonable measurement noise floor), or is there a flaw with this idea? Without the coil (dut) it (the fixture half) is electrically short and does very little, but with the right impedance the test fixture becomes a more efficient radiator..? this should only show up at the correct frequency with the correct loading coil (well I assume there are other antenna structures that can develop, its just the one I am familiar with)

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 01:55:18 pm
content: All of the phenomena you listed there are "linear" in the technical, mathematical sense of the word.Non-linear effects would include diode rectification, for example, whereIvsVis not a linear function.In this discussion, this is very important, since the algorithms used for open/short/load calibration of a reflection bridge assume a linear DUT.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 06:58:35 pm
content: Quote from: TimFox on August 28, 2022, 01:55:18 pmWould that mean that certain components would have different errors in magnitude on different fixtures even if properly calibrated (the EM radiation from the fixture that has its electrical length effected/altered by the DUT)? Am I correct in thinking that a particular structure is going to have a particular Z that makes it radiate well (by radiate well I mean a complex structure becoming a slightly more efficient radiator then usual), and that behavior can't be seen unless you have that particular thing (DUT) connected to that particular structure?

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 07:26:00 pm
content: Yes, any radiation that depends on the stuffafter the calibration planeon the fixture will change the calculated (after calibration) impedance.In an ideal world (approximated by a device-under-test sealed into a shielded structure resembling a BNC terminator), such EM radiation would not occur, but if you have, for example, flying leads external to the test fixture that will have a real effect.HP, and other vendors such as Coilcraft developed specific (non-cheap) fixtures to get reproducible results with different styles of components.I remember one from HP that produced the same binding-post locations as on their older 4342A Q meter.This may not give physically ideal measurements, but allowed direct comparison with data measured on 4342As.Going back to your original question about binding post fixtures, the center-to-center spacing is 0.75 inch, which corresponds to my measurements I referred to earlier, where approximately 15 nH appeared in series with the DUT due to the 0.75 inch length.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 07:44:17 pm
content: yes I noticed that the 15-20nH is showing up with different capacitor types of the same size when inserted as deep as possible into the fixture

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 07:49:45 pm
content: I think you can make some slightly better ones by doing some 3d printer castings or maybe braze something out of machined copper that attach to a BNC connector for shorter spacing between the leads. I want to make it so you put the DUT on top into notches with a hole, so that the capacitor lays in there and then you tighten two screws to hold it into placethat way you could measure stuff without bending thats perfectly in line with the fixture.Likeleads ====O==== DUT ====O==== leadsthe = sign is the notch, and the O are the threaded holes that the notch is cut into, so it would get held down with two screws, one pushing each lead into the notch. Or maybe you can just leave a heavy object with a thin plastic 'blade' on it to go into the notches with a U cut over the DUT so that it compresses the leads into the notches from the top, like the lead piston from Alien 3(imagine a test fixture like that BTW, drop the parts into little pools of liquid metal to make sure the contact resistances are good, damn all the complex geometry blades and collets and spring tensions etc)!I guess you can take a thin hack saw to a regular BNC to banana fixture to put a lenghtwise notch on it also, but I think I can make it smaller, then a series can be made for different parts.I bought marx brand taps a while back that go down to really small thread pitch (what was it, 0-72? Maybe I can cut that with a jewelers saw)I am thinking to get a BNC to copper ridgid tubing, cut a notch in the tubing to free the center conductor/dielectric, and bend it into a 'dipole' shape and build the DUT clamps on top of the split outer shield and the middle steel wire of the 1/4 RGwhateveritis coaxial cable. Maybe you can even take the forks in side of female header pins and solder them to both sides of the split coax to make 'forks' that you insert the leaded DUT into with a card on top to push it in with a little bit of weight, and built a plexiglass reinforcement around it to keep it stable.

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 07:58:18 pm
content: You might want to try different overall lengths, using a careful fixture, to see how that changes.My original fixture for SRF was two panel BNCs (through 2-oz single-sided FR4) wired together with two 50 ohm resistors in series, connecting the DUT from the junction of the two resistors to the copper.One BNC to the tracking generator and the other to the input of a spectrum analyzer to find the frequency of minimum transmission (series-resonance of the DUT).By the way, I mis-remembered the impedance of the MCL transformers that I used years ago before retirement.In their current catalog,https://www.minicircuits.com/pdfs/TT25-1-KK81.pdfhas a 25:1 impedance ratio, for 1250 ohms at the secondary (not 13 k).The package is equivalent to a DIP with 0.1" spacing.That unit is rated for 0.1 to 10 MHz at -1 dB.Others with lower impedance ratios, e.g.https://www.minicircuits.com/pdfs/TT4-1A-KK81+.pdfare available with 4:1 (200 ohms), rated for 0.3 to 180 MHz at -1 dB.

author: G0HZU
author_rank: Super Contributor
timestamp: August 28, 2022, 08:01:44 pm
content: If you want to explore the limits of a good VNA then you should abandon BNC based test fixtures. Taken to extreme it's possible to measure SMD capacitors with good results. See below for an old plot of a SMD 10pF cap compared to a model of a 10pF cap in series with 0.6nH package inductance. The agreement for capacitance vs frequency and self resonance is very good.You can see the VNA also did a reasonable job of measuring the ESR at around 0.1 ohm all the way up to 2GHz.This was taken with a decent lab VNA and a good cal kit and an 18GHz rated test fixture. I've got a lot of experience doing stuff like this including taking s-parameters of SMD transistors up to many GHz and this requires a really good VNA and cal kit and test fixture. Using a BNC based system is OK for casual tests but a good VNA is capable of a lot more with the right setup.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 08:04:42 pm
content: This might be easy to make today. I think I have all the parts. Just need to make sure the resistor can fit inside of the female header forks, at least some of them should. I think you can make it very compact.Would this in general be better if you had a ring of copper with the center conductor floating above it, or is it a better as a 'tiny' dipole? (i.e. strip coax, solder a ground plane ring around it, then bent the center pin so its floating above the ground plane, and mount the forks at an angle (insertion would be weird).I think the removable fixture design/build will be fun anyway, even if SMD is better

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 08:32:10 pm
content: To test such a fixture, which requires a 50 ohm load along with a short and an open, you can use other resistor values (I suggest 15 and 150 ohms for a first test) after calibration.Since you are avoiding SMT, what do you intend to use as a 50 ohm load for calibration?You need to mount the short and load at the same "plane" as the DUT for an accurate calibration.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 08:44:46 pm
content: Oh yeah I have been trying to find RF resistors that are through hole but the Vishay ones that supposedly go to 3GHz are not in stock without 1000 quantity. There appear to be other dealers selling them but its Taiwan.. not sure if its a good ideaThis is the part I thought might be a candidatehttps://www.vishay.com/docs/28769/mbasmahf.pdfavailable in 50 ohms to 1%

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 09:09:14 pm
content: The Vishay metal-foil resistors, such as RNC90Y, are relatively low in parasitic capacitance and inductance. eBay:https://www.ebay.com/itm/172408923513?hash=item28245f6579:g:upIAAMXQh8NTeDZl&amdata=enc%3AAQAHAAAAoDBU5HDSD1AGI%2FLN8%2FttY44bntkl4idURG%2F9Kz38059bOHUGvw4ubZeEn1s4hvDVO53osTjiQ1YvdEPlXtHn6Dz9udh9CbJ78da4%2BGa5ljjSsD4bliLoPBt821OfJr9E8QbH31Z41aYII8bqw4fOh8GiCZImok5ma5u56oT7OCoaMT7ievtsryFZpcdfuw%2BU4NcPvPAjDjFszNx52o5GNNY%3D%7Ctkp%3ABk9SR6CFx-TcYAAlso, Caddock has leaded resistors with a serpentine pattern to minimize inductance.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 09:17:24 pm
content: I have some of those (maybe even a 50 ohm one), but I never found a impedance related plot for them.

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 09:26:54 pm
content: Some data on the S555 series:http://www.vishaypg.com/docs/63007/RNC90x_63007.pdfNote footnote (3) about inductance being dominated by leads.The values are max or typ for the entire series, regardless of resistance.I assume without proof that at 50 ohms, the inductance is lower, but still dominated by the leads.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 09:42:34 pm
content: Weird, I found some graph about foil resistors and it looks like they start having a Z/R ratio that goes 'bad' at around 10-20MHz, while the RF resistor I found in the PDF has the same thing start to happen at 1GHz for similar values. I wonder if they are not measuring them equally or something like that.https://music-electronics-forum.com/filedata/fetch?id=910380&d=1539381835thats where I got the graph, it says its from univeristy of iowa. I put the pictures of the resistor for reference by myself, its not said in the PDF what package it is. But the Y axis is the same idea I think. I wonder what... I assume the data sheet graph is starting at 100MHz.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 09:52:51 pm
content: this may be relevant:https://www.viking.com.tw/en/news/New-Product-CSRF-Series-MELF-High-Frequency-Resistor/viking-news-016.htmlCSRF series is a MELF resistor specially designed for high frequency applications. The general type MELF resistor uses a spiral trimming method to increase the internal inductance, CSRF uses a special non-spiral trimmed method reduced the internal reactance which caused the impedance change when the resistor used in high frequency applications, so it is very suitable for high frequency circuit design. Something to do with helix vs planar construction?

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 09:56:39 pm
content: As continually pointed out in this thread, the actual measured value from a practical component at high frequencies depends critically on the fixturing.You misread the x-axis on the foil graph: your "bad" region for 100 ohms is 100 to 200 MHz, not 10 to 20 MHz.The graph of the foil resistor impedance is suspicious: 0.5 pF (typical value for RNC90Y style resistors) and 50 ohms will be 70% of full impedance (equal magnitudes of resistance and parallel reactance) at 6.4 GHz.I leave the calculation of % impedance at 200 MHz as an exercise for the reader.On the axial component, note that for 50 ohms and below the error is inductive, while for 100 ohms and above it is capacitive.

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 09:57:45 pm
content: Quote from: coppercone2 on August 28, 2022, 09:52:51 pmThe MELF looks good, but I thought you didn't want SMDs.Components like this are probably tested using a fixture similar to those shown in the Coilcraft catalog.https://www.coilcraft.com/getmedia/b114ada6-5ca1-4101-b9dc-7ce88ee145c2/smfixtur.pdfWhen we bought a 4191A from -hp-, they recommended one of these for SMD components.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 11:00:09 pm
content: well at least the MELF package is round so its alot more acceptableit looks like my idea is very similar to the AXL-A fixture from coilcraft. I am close to finishing a spot welder and I think I can spot weld some leads on the MELF package to make a normal resistor, maybe.

author: TimFox
author_rank: Super Contributor
timestamp: August 28, 2022, 11:02:11 pm
content: The MELF is a good package for critical SMT components.I found them to be often less magnetic than other packages, when I was working in NMR.However, 1206 package thick-film resistors are reasonable to work with and far cheaper.You only need to start with thin tin-plated wire (say, #26 AWG) and solder to the already-tinned ends of the 1206 package, and you now have a leaded part.Much easier than spot-welding.

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 11:04:19 pm
content: oh right I see they shifted a 0 down so it says 10 twice lol

author: coppercone2
author_rank: Super Contributor
timestamp: August 28, 2022, 11:09:03 pm
content: I want to try winding coils around them though so round and 1/4 watt + is preferred

author: profdc9
author_rank: Frequent Contributor
timestamp: August 29, 2022, 07:45:44 pm
content: I designed and built a VNA herehttp://www.github.com/profdc9/VNAI included a PCB with a fixture for discrete components based on a ZIF socket. It seems to be fairly accurate up to at least 200 MHz.https://github.com/profdc9/VNA/tree/master/fixtureIt can be calibrated with a wire a few mm long, an open circuit, and a 50 ohm thin film metal resistor inserted into the socket. The VNA uses an algorithm described in the documentation to do a one-port calibration, or a two-port if you wish to test that way.

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2022, 08:39:53 pm
content: I think a better calibration would be had if instead of a wire you use a flat sheet of copper attached to the top of the wire at the dimension of the ZIF sockets but I am not sure, or maybe if you hammer out a wire to make it flat in the middle around the two bends (it must look like a staple) to make it a rectangle that matches the zif pin dimensions? Or just bend a thin sheet of copper into a staple shape. I kind of wonder which one works the best, maybe it is infact the wire of the correct dimension without any flats?

author: TimFox
author_rank: Super Contributor
timestamp: August 29, 2022, 09:39:20 pm
content: The best “short” calibration is a “cap” or disc to minimize inductance, rather than a straight wire. In the extreme example discussed above of 20 mm wire length, roughly 15 nH, the inductance would have +j 50 ohms reactance at 530 MHz, and you can scale from that.

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2022, 01:17:23 am
content: for a dip socket might that look like a disk capacitor/mov made out of solid copper? or would you want a disk that sits in the socket like a small flying saucer landed (like a solid photoresistor)?

author: TimFox
author_rank: Super Contributor
timestamp: August 30, 2022, 01:56:46 am
content: The DIP socket is not ideal: best is something shaped like the BNC shorting cap with a center conductor connected to a cylindrical shell, grounded all the way around.If not cylindrical in nature, you have a small inductance that may be acceptable, depending on wire length and frequency.There is a lot of literature on the inductance of lead and bond wires.

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2022, 02:10:31 am
content: it makes me want to braze a staple to a old penny for the ZIF socket

author: jonpaul
author_rank: Super Contributor
timestamp: October 03, 2022, 05:29:08 pm
content: in our research for digital audio transmission we use HP4194A with 41952 impedance fixturesFine résultats 100k to 500 MHz with genuine HP / Yokogawa test adapters.Can measure 0. 3 pfThese are all unbalanced, no transformers can be used without affecting the results.See HP4195A spec, app notes and HP long note on impedance fixtures and measurementhttps://www.keysight.com/us/en/assets/7018-06727/brochures/5965-4792.pdfJon

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2023, 06:40:25 am
content: I have a APC-7 to bnc adapter. I put a single piece old school bnc to banana adapter on it.If you are curious, with this addition, after calibration at the port, it reads like 6pF at 1MHzI also got the resistors (those 50 ohm RF leaded ones) finally.The 16092A fixture, reads picofarads above say.. 10 MHz (under that it reads inductance open circuit). The measured value is ~1pF up to 1 GHz, even if its rated for 500MHz. It gets more resolution as you go up in frequency. I tried putting those 50 ohm resistors in there before, but its annoying because I don't have the other half of the fixture for through hole parts, and I feel like its going to get damaged. its priced scandalous on ebay. It was sitting for a while now, not cleaned at the test point,when i connected it shorted, it read 300 miliohms at 1MHz. I had it read down to 20 Miliohms before. I have a feeling its the instrument and not the fixture. Maybe I should replace the center pin of the APC-7 connector. I might try a short duration electroclean on the gold stuffcleaned it very well and recalibrated with everything cleaned. Now its repeatedly giving ~12 miliohms short circuit on the 16092A fixture at 1 MHz. The short circuit value bobs up and down by maybe 2 mili ohms on the fixture. I wonder if its supposed to be dead stable. Maybe its better if the machine stabilizes, this was a test with maybe 10 minutes of on time. I don't want to leave this machine alone since I saw the shuffer cap start smoking in it! ill have to park my ass down there to do a real warmed up test.If you are interested in deoxit gold, the difference in the test fixture between clean and then swiped with deoxit on a chamois wipe is not visible.The APC-7 to BNC adapter by itself reads 3pF, rising to 15pF at 1GHz when openThe APC-7 to BNC with the BNC to Banana (the shorter one that rotates the whole body into position, without a slip joint) reads capacitance to around 625MHz, then it goes inductive. But its alot of capacitance at that point.When I put the 50 Ohm resistor in it, I get a phase shift of like 0.04 degrees at 1Mhz. At 100MHz the phase shift is 7degreeWaiting for the 93 fixture with banana connector and also the shorting plate that goes under the test fixture.Just through those measurements might interest people that were interested in what they actually see on the equipment when its used..The difference between the narrow band load in the APC7 mechanical cal kit and the wide band APC-7 load that was a random purchase is something like 0.2 ohms off from 50. A bit over at low, a bit under at 1GHz.Is looking at the capacitance of the adapter a good way to determine if there is "too much crap"?

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2023, 10:06:57 pm
content: if you are curious about electrocleaning the gold fixture stuff with alkali cleaner, basically the discolored smut on the surface of the fixture turns black. If you let it bubble a bit some will come off . Then if you wash it and gently rub it with baking soda on your finger it comes out looking nice and goldlike you can put baking soda paste into it after cleaning an swirl a q tip around in there and the inside comes out looking fresh. no pressure just slurry moving aroundthe apc-7 connector bit took a few alternations. I bet if you apply any sort of pressure in there, it will also clean up nicely, but it seems kinder to the part to use electricity and just slurry flow rather then hard abrasive scrubbing

author: coppercone2
author_rank: Super Contributor
timestamp: September 23, 2023, 11:42:13 pm
content: I got the 125MHz test fixture 16093B and cleaned it as aboveIf you are curious about what you will see:At 125MHz (the rating) the OC impedance reading is 250 Ohms.With the APC-7 to BNC to banana jack kludge, the impedance reaches 250 ohms at ~77 MHz.By going with that metric, that is... what is the maximum impedance you can measure at what frequency, the performance is roughly doubled by using HP test fixture.also beware the spring clip test fixture. alot of them on ebay have broken acrylic bushing. the APC-7 center pin is loose then. thats why my short circuit impedance readings were shit, the seller deceived me with creative backwards pictures. I used the APC-7 gauge and it was giving me odd readings that were inconsistent. the plastic bit is smashed and it was shifting. What a fucking dick wad

author: jonpaul
author_rank: Super Contributor
timestamp: September 26, 2023, 04:01:24 pm
content: Coppercone, we had a lot of experience with HP 4195A and the impedance test sets and fixtures.You can occationally find these off epay, at costs perhasp $100..500.The original vinatage HP/Yokogawa Japan fixtures are APC and interface to other analyzers besdies the 4195A.The SMD, binding post and otyher fixtures are the best.We used the system since 1992 in our transformer developent to 500 MHz.Enjoy,Jon

author: coppercone2
author_rank: Super Contributor
timestamp: September 26, 2023, 09:07:28 pm
content: did you do any calibration at the fixture save for electrical length setting?I.e. use calibration grade 50 ohm SMD/leaded resistor, some kind of short circuit (golden block), open circuit (acrylic block)?For calibrating a 50 ohm on the banana / screw terminal jacks, you would need a much longer 50 ohm resistor. I have seen these in a old HP amplifier. Like a thin long resistor that basically fits between the jacks with no leads. Or some kind of clever resistor soldered to low impedance bus bar to put into the through hole fixture.I.e. do you have a part # for a calibration grade RF SMD 50 ohm resistor?I got RF resistors that say they are good to 3 GHz (sprial cut) and 1% accuracy @ 50 ohms. They have leads. I kind of wonder what accuracy I am getting if I perform a calibration at the screw terminals with custom standards (say a copper strip, the resistor and nothing) to get extended bandwidth from the fixture.

author: coppercone2
author_rank: Super Contributor
timestamp: September 27, 2023, 03:50:21 am
content: also have you used the temperature test fixture ever?I don't understand the high temp fixture HP has. At first I thought the ceramic looking thing might be a heat conductor, but it looks like the fixture itself is expected to go into a oven or something? I don't see any power connections or heaters in the diagram.What I thought might work is to have a glass tube covered in a fiberglass braid blowing hot air from a hot air station on a through hole part. Then to some how measure the part. I assume this would need to be a thermal camera. I thought that maybe you can put a tiny dot of black paint on it, then use a thermal camera with a zoom lens to zoom in on the painted spot to measure temp. I have the seek thermal, which I built a stand for that has a remote cable. That way I can put a i phone on top of the IA so I can get a temp readout while I am looking at the instrument readout.I thought this might give a reasonable temperature test for a leaded component.

author: jonpaul
author_rank: Super Contributor
timestamp: September 27, 2023, 04:58:48 am
content: Cu:This topic could be moved to from RF to Measuements group. I would also post to Groups.io>>HP forum.So, what is the C/L/R min/max you seek to measure .... what is your objective?We have HP 4195A (similar to 4395A) and 4275A RLC, as well as Wayne Kerr 3245 inductnce analyzer. HP 4195A may be similar in some test fix and CAL/See complete app notes and manual on the analyzers, test sets and fixtures for CAL info.Best gen ref is the classic HP/Keysight Impedance Measurement Handbook A Guide to Measurement Technology and Techniques 6th Editionhttps://www.keysight.com/us/en/assets/7018-06840/application-notes/5950-3000.pdf1. Every Impedance/Network/RLC requires a full CAL for specified accuracy over the band.Open CktShort CktZo 50 Ohm2. Each test fixture kit includes an APC-7 or other calibration open/short/Zo standards.3. After full CAL the analyzer will process the CAL for each freq.We leave the Zo 50 Ohm in place and check for flat 50 Ohm - j0 across the band eg 100 kHz..500 MHz.4. All DIY CAL attempts at open/SC/Zo will be OK at LF but have some L or C > 5 MHz.5. We get pure Cu sheet 10..32 mil and small flats, have then Au plated to make DIY SC eg for SMD fixt.6. We have never used the HP high temp test fixtures, as our transformers have little change with temp.7. Some LCR bridges have a lead legnth comp or switch eg 0.5 m or 1 m lead comp.8. With HP 4195A, full CAL at 100k..500 MHz we easily measure 0.3 pF cap Pri..Sec in a guarded shielded transformer.At these low C, a ridgid setup is required for repeatibility.Hope this info is interesting.Bon Soiree,Jon

author: coppercone2
author_rank: Super Contributor
timestamp: September 27, 2023, 05:11:08 am
content: I have the 16092 and 16093 fixtures and the APC7 mechanical calibration kit with all the things in it. But the machine only calibrates at the connector with the APC-7 open short load, and it accepts electrical length for the compensation, and you can use the little grounding spring/bonnet.the 3 terminal binding post fixture is 125MHz max. The two terminal one is 250 MHz (don't have it), and the SMD one is 500MHz.What I am curious about is with the correct standards, can the maximum frequency of the fixtures be increased. A short and open for the SMD test fixture seems doable, it would just be a metal block like a SMD resistor and a acrylic/ceramic block of the right size. But then the load would require a calibration grade SMD part. Does this exist? Are there other parameters of the fixture, besides lack of standards, that limit the frequency?I.e. if you got metal and dielectric blocks the same size as a 1210 component, and a really good 1210 resistor, could the maximum frequency of the fixture be pushed past 500MHz?And also curious, if you did the APC-7 load calibration, but did the open and short calibration inside of the fixture (with custom standards the size of the component you are measuring), could this some how increase accuracy, or will it just get messed up? I assume it won't work, but I don't know exactly how it works (very complicated). That way your open and short is nearly perfect, but the load (due to lack of a calibration resistor) is done conventionally, without the test fixture installed. And if someone knows, it would be interesting to know what the machine actually calculates if you did the open and short in the fixture but the load with just the connector. Even if its totally worse, I just wanna know what happens if you do this. I assume part of the problem is the electrical length correction, which would be applied to all 3 terms, but it would only be required for the load, not the open or short? i.e. if you did O/S cal in fixture, it would still assume the electrical length is 0.34, even though its pretty close to 0 for O and S, but actually 0.34 for load, since its not part of the fixture if done that way.?

author: jonpaul
author_rank: Super Contributor
timestamp: September 27, 2023, 05:43:27 am
content: Cu: AHA! Now understand you points better. Please reread my edited last response link.1/ The BP and SMD adapters indeed have only a SC included.2/ CoilCraft has done extensive work in exactly this area with the same test sets and fiztures.See their excellent notes on standards for CAL.3/ Our 4195A is speced to 500 MHz max and no work can be abouve that freq.Other similar like 4395A may go higher.4/ The test fixtures for impedance have transformers, bias nets and other components that are limirted in freq.41952A is 100 kHz..500 MHz only.JonPS: Excellent Coilcraft app notes may have some relivance to your issues on calibration:https://www.coilcraft.com/en-us/resources/application-notes/

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2023, 12:45:10 am
content: the next SMD test fixture came in, this one also has damaged acrylic. Instead of letting it fall apart like the other one i dripped about 0.075 ml of weldon #4 acrylic cement on top of the cracking acrylic with a syringe.Hopefully it seals any damage. In a week I will test with APC-7 gauge to see if pin did not shift.This acrylic APC-7 test fixture dielectrics seem like a time bomb. I wonder if you can replace it with 3d printer.

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2023, 03:50:15 am
content: Well I got a question, it says the spring thingy could be used to cancel residual L+R. Determined I should not wait a week because I am so boredWhen I put the fixture together and short it out with the spring gold elbow thing, the inductance at say 50MHz reads something like 0.6nHWhen I put on the grounding skirt/terminator, the inductance actually reads higher, at ~1nHIs this correct or is something messed up?I figured when you screw the skirt on, the inductance would be lower then the fixture shorting itself. But it turns out that if I did cancellation, I would get negative inductance.Is it only for use with a part and the methadology breaks down with a self short circuited fixture?Like, if I store the ground terminator values, then actually measure a part, it will be more accurate, even if it does not agree with the fixture being shorted out by the gold spring loaded elbow piece?At 500MHz1) test fixture shorted by itself : 1.1nH + 100-120 mili ohms resistance (varies)2) test fixture shorted by grounding terminator skirt : 1.58 nH + 75 miliohms (very repeatable down to maybe 2 miliohms).So the L is higher but the R is lower on the L + R measurement.is this right? why the hell is residual inductance higher with the special shorting terminator then with the shorted fixture. Is shorting the fixture by itself some how bogus and or has a error?Like just looking at it, when I see the fixture gold angle block pushed up against the post with the spring, it seems to me like the inductance has to be lower then with the skirt. The skirt is like big, it fits nicely but its still the size of a coin. I don't think the measurement is incorrect. Is it just a general case? Or is it only meant to be used with the 2x clip, rather then the plunger?'https://www.picclickimg.com/ZWQAAOSw7K5kqcHM/HP-Agilent-16092A-Spring-Clip-Fixture.webpI just can't see the grounding skirt having a lower inductance then the shorted plunger?! I could understand that the skirt has a lower resistance, since there is like 30 points of contact, rather then some angle piece being wedged against a post.. but inductance just must be higher no matter how wide you make it because its damn big. You could make it 1/2 as big and it would still work. Its over sized as far as I can tell.And yes its the correct one, I know there is a different skirt for the binding post fixture. This is the skirt for the 92A, not the 93. Infact I would call this a ball room gown from the 1300's of spain, not a skirt. This skirt would be more then modest even in the 1800s. Explain this to me. Why is it so big. its the size of a quarter but you can probobly make it the size of a dime.And the plunger/gold angle is fine, I have a few of them now because of failed aquisitions. They all read very similar when I swap em.Is the grounding skirt only for the 92A fixture configured with the big top slide piece and NOT the plunger, or should it be used anyway for real parts measurements?!

author: jonpaul
author_rank: Super Contributor
timestamp: September 28, 2023, 06:15:41 am
content: Dear Cu: fine questions, I cannot help....I Suggest you pose this question with pix athttps://groups.io/g/HP-Agilent-Keysight-equipment/topicsThat forum has HP afficiandos and ex HP retirees. They can help....mention the analyzer (4195A?) and test fix #s.As I have 4195A and different fixtures, I cannot assist.In practical transformer deveopment to 500 MHz, inductance >> 1 nHOur C meas. is down to to 0.3 pF.Bon chance,Jon

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2023, 06:51:55 am
content: lol that is the email box killer websiteHopefully someone here measured the skirt ground on the 4191A.I am guessing its because if there is a part, it will be high up pinned against the center post, so the whole inductance will be factored in, and when the angle piece is wedged against it, its near the base, bypassing the majority of the expected inductance.Like it might be 2-3 mm off the ground, but the shorted fixture might be making contact 0.1mm off the ground. Unrealistic conditions for most parts save maybe <0201

author: jonpaul
author_rank: Super Contributor
timestamp: September 28, 2023, 11:14:02 am
content: Cu:" lol that is the email box killer website" (Groups.io)have sued many forums in Groups.io for years no issues with spam etc.Like any forum or site (incl EEVblog) one must tweak comm parameters as the defaults often have a lot of useless nagsa sent via email.Easy also to hide your real email adr.Found many great connections and deals on groups.ioj

author: coppercone2
author_rank: Super Contributor
timestamp: September 30, 2023, 02:51:42 am
content: I wonder if there is a neon element that I can plug in that would function at 40VDC to measure impedance of it

author: coppercone2
author_rank: Super Contributor
timestamp: September 30, 2023, 06:09:00 am
content: Quote from: jonpaul on September 27, 2023, 05:43:27 amWhat is the limiting element on the spring clip test fixture? I took it apart, there is just gold plated things.Also, I got a HP balun thing, for measuring differential impedance. I see there is alot of options available for higher frequencies. I guess it might answer those burning questions I had about twisted pairs though. I just can't sleep at night thinking about whats going on when you twist some wire together. How could anyone given all the shenanigans around wire insulation properties and how neat your twist is.

author: coppercone2
author_rank: Super Contributor
timestamp: October 03, 2023, 05:27:16 am
content: got the transformer. I tried a twisted pair of 18 gauge banana alligator clip cables that I loosely twisted.Short circuit was 8.4 ohms, open circuit was 412 ohms. I believe its (OCR*SCR)^(1/2)I got 58.8 ohms @ 1MHzIs this right? why the hell do I need to know the impedance of a twisted pair anyway?!. What the hell am I going to do with this information?But actually, how do I do this right? The balanced impedance is 100ohm, the unbalanced impedance is 50 ohm.I am guessing I do the OSL calibration with 100 ohm instead of 50 ohms on the load?When I measure 100 ohms, it reads as about 50. So my cable impedance is like 58.8*2, or 117.6 . Maybe I will go through seeing how calibration changes things when I construct a good 100 ohm load. who else is super excited about cable impedance?