Probe into probes.  What's up? - Page 1
Forum section: electronics / testgear

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 07:31:02 pm
content: I recently received an inexpensive ($36) no-name 500MHz probe I got of Amazon (called a P-6139A of all things)and I thought I'd compare it to some other probes I have arornd here including my genuine Tek 6139A probes.First off, the probe seem very well made. The cable is very flexible (even more so than the Tek probes), the compensation/BNC housing is metal and it has the 10:1 auto-select pin. The BNC fist my Siglent scopes and Tek very snugly and the accessories all seem to work very well. Construction is modeled after the Tek probe with the insulating sleeve going all the way to the probe tip and unscrewing in a similar way to the Tek. The tip does not unscrew from teh cables assembly though. It's rated a 300V CAT II and 9pf @ 10Mohm.In any case, using the Bodnar pulser and my own 1.2ns pulser I did some rise time trials with it, the Tek 6139A and a Hantek PP300 (300MHz probe). The results have me a bit puzzled.The first two screen shots are of my and the Bodnar pulsers feeding directly into the "improved" SDS2104XP scope. In both cases we can see a fairly nice and consistent square wave.Next 2 are the Hantek PP300. This is about what I'd expect for this $20 probe. Actually pretty nice for the price.Nest 2 are the Tek 6139A. WTF? while the initial part of the leading edge is sharp and fast, something goes awfully wrong about 65% of the way up. Does anyone have idea what this is about? I get the exact same result from the other two Tek 6139A probes I have here.The next two are no name P-6139A. The result with the Bdonar pulser is almost identical to the Tek probe! Again, what's going on? The result with my pulser is also weird but could be due to soem interaction between the pulser and the probe. It still starts out okay, but seems to give up steam before the Tek probe does.I honestly expected a that at least the Tek probe woudl do better than this and I can't explain why the faster probes behave this way. Any ideas?

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 07:33:37 pm
content: The rest of the screen shots...

author: bdunham7
author_rank: Super Contributor
timestamp: January 31, 2023, 07:38:36 pm
content: Quote from: BillyO on January 31, 2023, 07:31:02 pmGroup delay...have a close look at the Tek 6139A datasheet.Edit: are your screenshots labelled correctly?

author: jonpaul
author_rank: Super Contributor
timestamp: January 31, 2023, 07:43:59 pm
content: Seehttps://www.tek.com/en/documents/whitepaper/abcs-probes-primerAlso Tektronix Circuits Concepts book Oscilloscope Probe Circuitshttps://w140.com/tekwiki/images/6/62/062-1146-00.pdfOscilloscope Probe Measurementshttps://w140.com/tekwiki/images/1/19/062-1120-00.pdfAny scopes avail as second test besides the Chinese?Any photo of test setup? Block/schema?Your Probes uses bayonet/BNC adapter or just ordinary ground cable/alligator?The self inductance of the ground return can affect transient resp, ringing, etc.We found P6139 rather delicate and use mostly P6137 x10 and P6136 Zo probes on our TEK 2465/P2467BThese probes are fine on Yokogawa digital scopes DL7440, 1740.Jon

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 08:01:54 pm
content: Quote from: bdunham7 on January 31, 2023, 07:38:36 pmYes. Why?

author: tautech
author_rank: Super Contributor
timestamp: January 31, 2023, 08:06:02 pm
content: Quote from: BillyO on January 31, 2023, 07:31:02 pmDo Tek 6139A probes have a hidden (not obvious) HF adjustment ?The manual doesn't mention such.https://download.tek.com/manual/063087005.pdfAll the Asian 500 MHz probes I've seen had LF and HF trimmers.

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 08:07:04 pm
content: Quote from: jonpaul on January 31, 2023, 07:43:59 pmUnfortunately not, except my old Tek 465.Quote from: jonpaul on January 31, 2023, 07:43:59 pmA photo can be supplied .. but see next answer.Quote from: jonpaul on January 31, 2023, 07:43:59 pmPulser->BNC to probe adapter -> probe.Quote from: jonpaul on January 31, 2023, 07:43:59 pmNo ground wire used. Connected through probe adapter.

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 08:09:38 pm
content: Quote from: tautech on January 31, 2023, 08:06:02 pmThey do. Two of them. But how likely is it that the adjustment it is exactly wrong the same way on 3 Tek probes and one Asian probe?

author: tautech
author_rank: Super Contributor
timestamp: January 31, 2023, 08:11:09 pm
content: Quote from: BillyO on January 31, 2023, 08:07:04 pmSomething's not right.Some waveforms 0V is not on the 0V channel level like they're in AC input mode.

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 08:21:06 pm
content: Quote from: tautech on January 31, 2023, 08:11:09 pmThe Bodnar outputs an AC signal.

author: bdunham7
author_rank: Super Contributor
timestamp: January 31, 2023, 08:29:54 pm
content: Quote from: BillyO on January 31, 2023, 08:01:54 pmThe first screenshot in your second post is labelled "Tek 6139 Bodnar" but the scope is set to DC50 input....

author: tautech
author_rank: Super Contributor
timestamp: January 31, 2023, 08:34:03 pm
content: Quote from: BillyO on January 31, 2023, 08:21:06 pmOkay yeah, missed one waveform was 10 MHz and the other 20 MHz.Pop the lid of the compensation box and have a squiz at what's in there.You might need to download the old book on Tek probes to follow the schematic of how these were constructed.https://w140.com/tekwiki/images/6/62/062-1146-00.pdf

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 08:35:42 pm
content: Quote from: bdunham7 on January 31, 2023, 07:38:36 pmI can't seem to find this. It no longer seems to be on the Tek site and nothing else I have found makes mentions the group velocity characteristics.I guess you are suggesting that the different frequency components of teh sharp square waves will have different velocities in the probe system?

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 08:38:16 pm
content: Quote from: bdunham7 on January 31, 2023, 08:29:54 pmNot that I can see. It says DC1M.

author: bdunham7
author_rank: Super Contributor
timestamp: January 31, 2023, 08:38:40 pm
content: Quote from: BillyO on January 31, 2023, 08:35:42 pmYes, exactly.https://w140.com/tekwiki/images/a/af/063-0870-05.pdf

author: David Hess
author_rank: Super Contributor
timestamp: January 31, 2023, 08:38:55 pm
content: Because of the lumped input capacitance and response of the high impedance input, the high frequency transient response of the probe itself is used to correct the response of the oscilloscope. Tektronix did not include external adjustments for this, and instead released a different A/B/C version of the probe as newer oscilloscopes were released.More general purpose probes, like fromTexaswho also OEMs probes for Rigol and Keysight, include access to the high frequency transient response adjustments.

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 08:50:04 pm
content: It's trivial to get into the HF compensation adjustment on the P6139A. There is also another device in there. Not 100% sure what it is.

author: bdunham7
author_rank: Super Contributor
timestamp: January 31, 2023, 09:24:02 pm
content: Quote from: BillyO on January 31, 2023, 08:38:16 pmIs the forum mixnig photos again?

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 09:30:31 pm
content: Must be. That's not even the Bodnar. It's my pulser and it's straight into the scope.

author: bomp
author_rank: Newbie
timestamp: January 31, 2023, 10:46:02 pm
content: Does the Bodnar pulser need a 50 ohm load when the 10:1 probes are used?

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 11:26:02 pm
content: Quote from: bomp on January 31, 2023, 10:46:02 pmShouldn't, as it's not driving a 50 ohm transmission line.

author: BillyO
author_rank: Super Contributor
timestamp: January 31, 2023, 11:42:39 pm
content: Here are soem more images.The No-name P6139ATwo pictures of the Tek probe disassembled. In the picture where I have the metal case apart you can see the two HF resistors at the bottom. The LF compensation is near the center and There is that blue object just above it and to the right. It's marked C2, but there is not way to get anything into it to adjust it. It may need a special tool.The last picture is the tesr setup with the Bodnar. It's exactly the same with my pulser too as it's just about the same size.

author: srb1954
author_rank: Super Contributor
timestamp: February 01, 2023, 12:50:46 am
content: Quote from: BillyO on January 31, 2023, 11:26:02 pmI don't know what terminating load the Bodnar pulser requires but the conditions for verifying probe performance traditionally calls for a 25source (ref. Tektronix Circuit Concept series, Oscilloscope Probe Circuits, p27). This source impedance is typically made up of the pulse generator source impedance of 50paralleled by a 50through termination. So even if you are not using a interposing cable the output of the pulse generator still requires a terminator.

author: tautech
author_rank: Super Contributor
timestamp: February 01, 2023, 01:12:40 am
content: Quote from: srb1954 on February 01, 2023, 12:50:46 am100%If it weren’t for a darn power cut I’d put some screenshots up showing exactly this.

author: BillyO
author_rank: Super Contributor
timestamp: February 01, 2023, 01:16:06 am
content: I could certainly try that.Edit: Well! That just made one heck of a difference! This is more like what I expected. With the Tek probe being the best the Hantek the worst and the no-name 6139A being in between.So that Hantek 300MHz probe is really a 300MHz probe. The no-name P6129A looks like it would come in around 400MHz and the Tek's rise time is exactly what I calculated it should be @ 500MHz. Nice.Shot in the same order as before: Hantek, Tek, No-name.

author: bdunham7
author_rank: Super Contributor
timestamp: February 01, 2023, 01:29:30 am
content: Quote from: srb1954 on February 01, 2023, 12:50:46 amIf you were characterizing the probe and wanted to fairly assess whether it met its specifications for BW, etc, this would be correct. However, if you are just probing some circuit, you have to take it as it comes. My Tek P6139A looks entirely different thenBillyO's, so I can't demonstrate with that. However, if you try it with a P6156 500R 10X, it looks good either way and just the amplitude changes. The reason 25R matters is that with 8pF and 500MHz, you get a calculated Z of only 40R, and of course the actual impedance of the probe is fairly complex at that point. I doubt that this signal is going to magically clean itself up with an extra 50R terminator, but I'll wait and see the result.

author: BillyO
author_rank: Super Contributor
timestamp: February 01, 2023, 02:30:08 am
content: Results edited into reply #24.

author: bdunham7
author_rank: Super Contributor
timestamp: February 01, 2023, 03:42:13 am
content: Quote from: BillyO on February 01, 2023, 02:30:08 amThat certainly made a lot of difference, and if you were looking to measure the rise time (characterizing re a spec) it should improve. But is it really better or more accurate or do you just dislike the aberrations less?Here is a P6156 500R 10X and a P6139A (doesn't look like yours, has a thread-on attenuator and can't use a BNC adapter at all, so all probing done by hand) without an extra terminator and then with one.

author: tautech
author_rank: Super Contributor
timestamp: February 01, 2023, 03:52:42 am
content: Quote from: bdunham7 on February 01, 2023, 03:42:13 amNicely captured SMPS ripple on the max and min.LED lighting ?

author: bdunham7
author_rank: Super Contributor
timestamp: February 01, 2023, 04:07:47 am
content: Quote from: tautech on February 01, 2023, 03:52:42 amNo, my LED lighting is now completely quiet. Besides, if that's noise it has got to be up around a GHz or so given that I'm at 20ns/div. Those are all single-shots, so you see stuff you might not otherwise. Perhaps it is internal, maybe ADC noise?

author: BillyO
author_rank: Super Contributor
timestamp: February 01, 2023, 04:20:51 am
content: Quote from: bdunham7 on February 01, 2023, 03:42:13 amI think both to some extent. That document on probe circuits mentioned above states several times that Tek probes are spec'd and calibrated using a 25 ohm source and they make a point of mentioning finding low impedance probe points for HF signals.It's not really fair to compare a P6139 to the P6156 for rise time and susceptibility to source impedance, however I am scratching my head as to why your 6139 shows practically no degradation in rise time with the 50 ohm source. What source are you using (not that that would matter)? Also, what other modifications were done to you 6139?Since the scope itself would not be much effected by the source impedance through a 9M ohm probe, and it is responding properly to the pulsers when directly connected, then any aberrations must be in the probes. But they do behave fairly well when applied as suggested by Tek.In any case, the document discusses the circuit used in the 6139 on page 23 and gives an outline of the adjustment procedure so I now have a fairly good place to start with and see if I can improve things. However, I feel fairly certain I'm not going to get what you are seeing with you 6139 using a 50 ohm source.

author: bdunham7
author_rank: Super Contributor
timestamp: February 01, 2023, 04:35:35 am
content: Quote from: BillyO on February 01, 2023, 04:20:51 amI'm using the same Bodnar pulser. My 6139A is older than yours, has the threaded attenuator and is not made in China. It has not been modified that I know of. My guess is that the degradation doesn't get much worse because there isn't as much in the first place.I don't know if you can get the same results I do.David Hesssuggests that Tek is juicing the response of these to improve HF response of particular oscilloscopes they were used with, which in your case would be the TDS3000 series if I have that right. By 'juicing the response' I mean deliberately loading the circuit more at HF in order to make up for losses elsewhere. So in that case, the source impedance would have an even larger effect than might normally be expected.

author: jonpaul
author_rank: Super Contributor
timestamp: February 01, 2023, 11:19:45 am
content: Rebonjour a tous...very Fine thread, probes are one of my favorite tools..At >100 MHz the probe C dominates the impedance and thus the 10X high Z probes are not so good.1/ For 95% of our P6137 TEK are best. We found some NIB in orig case with all tips/clips/adapters.2/ At >100 MHz the Zo probes like P6136 are excellent, despite the 500 Ohm..5K load, only use on 50 Ohm input scopes.3/ My Easy and cheap wideband DIY:Thin 50 Ohm coax Rg175/U or similar , .5..1.5 MTerm to BNC one sideUse with short shield directOR insert series 450 or 4950 R at cable shield/tip to make a DIY Zo probe.4/ The TEK calibrate with the comp trim with a 1 kHz cal signal. Beware some scopes change CAL freq with time base (485?)5/ Active probes (diff/FET) are very rarely needed and can be easy to damage physically or electrically6/ In SMPS/EBU work, current is often more useful than voltage info.We provide small bus loops with Teflon tube insulation on a proto or SMPS PCB.7/Using P6021, P6022, and the DC Hall effect probes/amps P6302, 6303, AM502B.A fine passive current transformer is the very wideband Pearson CT, 410, 411, The very best and widest freq resp and current capability.Use a wire passed thru the toroid...Hope this is interesting!Happy probing!Jon

author: BillyO
author_rank: Super Contributor
timestamp: February 01, 2023, 03:59:19 pm
content: Could it be that my Bodnar is faulty, or at least borderline?Even if I feed it directly into the scope, the signal into 1M is very much different than into 50. See the shots below - 1M first, then 50. You can see the 1M rise time is many times longer, and there is that shift 66% of the way up the rising edge.@bdunham7, what does yours do in the same situations?

author: jonpaul
author_rank: Super Contributor
timestamp: February 01, 2023, 04:22:39 pm
content: used Leo Bodnar 40ps pulser for years.Rated only with 50 ohm loadNo spec for open circuit loadAsk Leo,Jon

author: bdunham7
author_rank: Super Contributor
timestamp: February 01, 2023, 04:59:22 pm
content: Here is 1M and 50R superimposed at the same vertical setting. The slew rate and rise times are similar until the 1M rise slows down. This is a function of the scope, the Bodnar pulser is fine. The pulser itself does not need 50R termination to put out a clean square wave, as I have demonstrated with the P6156 or could be demonstrated by using an active-FET probe.This is a good discussion to demonstrate the difficulty, or even futility, of trying to use passive Hi-Z probes above 200MHz or so. The Hi-Z probe will put a complex load on the source, causing the actual signal at the probe tip to be altered--which also can be demonstrated by using a P6156 or active-FET in parallel. HF probes specific to scopes will attempt to compensate for this to some extent so as to give the appearance of an enhanced system reponse. The dilemma is then to decide which lie you would rather be told--do you want the probe/scope system to reflect the actual waveform including the alterations caused by the probe load itself or would you like it to attempt to 'compensate' and attempt to show you what would be there if the probe were not in the system?

author: David Hess
author_rank: Super Contributor
timestamp: February 01, 2023, 05:11:05 pm
content: Quote from: bdunham7 on February 01, 2023, 04:59:22 pmManufacturers take that into account, but Tektronix and HP used different methods. I forget which was which, but one calibrated their probes to show the signal at the probe tip with the probe loading, and the other calibrated their probes to show what the signal would look like without the probe.

author: jonpaul
author_rank: Super Contributor
timestamp: February 01, 2023, 05:39:30 pm
content: bdunham7, David H, very fine notes.No pulse gen, Leo B 40ps, Tek PG506, PG502 or the many HP high speed pulse gens will supply the specified output without a 50 Ohm load.The problem of high Z probes and FET probes in wideband work isa/ Ground return lead inductance (must use a Bayonet probe tip or adapter)b/ Xc of probe capacitance at the desired frequency.Those two factors are slight at low F but enormous above 100 MHz.Here is a calculation of Xc impedance of the probe tip C1/ X10 probe, 15 pF probe tipXc = 1/2pi FC200 MHzXc = 1/(15 exp -9 * 6.28 * 200 exp 6) = 50 Ohms2/ FET probe, C= 3pFXc = 280 Ohms.Thus the entire raison d'etre, for the X10 or high Z probe is in question due to capacitance Xc.For accurate wideband scope use, we use either a Zo probe (P6136) into a 50 Ohm scope,OR make a 50 Ohm coax RG174/U direct to a 50 Ohm ckt or with 450/4950 series R for Zo probe.Just the thoughts of an old retired EE, using TEK scopes and probes since 1967!Have an ABSOLUTELY FANTASTIC day!Jon

author: bdunham7
author_rank: Super Contributor
timestamp: February 01, 2023, 05:57:04 pm
content: Quote from: jonpaul on February 01, 2023, 05:39:30 pmBut I showed it doing just that in my earlier reply #27....Quote3pF is better than 8pF, but a high-BW FET probe will be even lower. <1pF should give you similar results to the P6156 even without termination.

author: BillyO
author_rank: Super Contributor
timestamp: February 01, 2023, 06:05:47 pm
content: While certainly no P6156 I have always made my own Z0probes. Cheap and cheerful. I usually solder them directly to the DUT, but in this case I used a BNC connector.This one is 1m long, 500R. It looks like it's suffering from a little bit of reflection.

author: gf
author_rank: Super Contributor
timestamp: February 01, 2023, 06:58:37 pm
content: Quote from: BillyO on February 01, 2023, 06:05:47 pmYou can try a 500R/56R divider instead of the 500R series resistor. If there is a load mismatch at the scope end of the cable, then an additional source termination of the cable helps to dampen repeated back and forth reflections. You can also check the scope's 50 Ohm input with a VNA to verify that it is really 50 Ohm and ohmic up to say 1GHz.

author: bdunham7
author_rank: Super Contributor
timestamp: February 01, 2023, 07:02:05 pm
content: Quote from: BillyO on February 01, 2023, 06:05:47 pmEven the P6156 has a bit of ruffling in the first part of the signal which is related to the length of the cable and so on.Here is another comparison, the scope set for 50R vs the scope set for 1M with a 50R pass-thru terminator on the pulser.

author: Njk
author_rank: Frequent Contributor
timestamp: February 01, 2023, 07:43:11 pm
content: Sometimes, it's not only the pulse edge fidelity that matters. For floating measurements in an LV applications, I'd usually powered the scope from the battery (TDS3BAT), because using the math function for two channels would be less accurate (all the errors doubled). What is less expensive now, a battery or a super-duper floating probe?

author: jonpaul
author_rank: Super Contributor
timestamp: February 01, 2023, 09:40:49 pm
content: Njk:Wideband fast measurements (as in the posts above) are seldom done on battery scopes.In power/mains/HV work, indeed a battery operated scope is usefulThe differential probes are costly and seldom needed.In Over 50 years of work we used a simple setup:mains>>variac>>1:1 isolation transformerUsually a Staco or GenRad 3..20A variac and Signal 2..5 kVa 120/240:120/240 transformer.Then a normal grounded scope and NO diff probe.Jon

author: Njk
author_rank: Frequent Contributor
timestamp: February 01, 2023, 11:23:46 pm
content: Quote from: jonpaul on February 01, 2023, 09:40:49 pmSure, but all that stuff can form a bulky setup.I recall in a POTS line connected devices, the isolation strength requirement (between the line side and the SELV side) is of kV units, because of possible lightning strikes, etc. So in telephone modems, the common approach was to use a transformer. Later, the chips were introduced (pioneered by Silicon Labs, IIRC) that were using a capacitive digital link over an isolation barrier to communicate between the line part and the SELV part within the chip. And the last modem designs were transformer-less. I was thinking the same approach could be used to design a floating probe. Not of GHz BW, of course. A diff probe is totally different thing as it requires ground connection.

author: BillyO
author_rank: Super Contributor
timestamp: February 02, 2023, 11:29:50 pm
content: I had some idle time today and decided to do some bode plots on the tek and no-name probes. A bit pointless, I know, but .. I only have an "improved" SDG1032X so could only go to 60MHz. As expected they did just fine. The behavior at the end is due to the sig. gen.Top picture is the Tek, next the no-name and the last is the SDG1032X by itself.

author: David Hess
author_rank: Super Contributor
timestamp: February 03, 2023, 12:15:29 am
content: Quote from: jonpaul on February 01, 2023, 09:40:49 pmBut battery powered oscilloscopes commonly have galvanically isolated input channels, making them particularly useful for wideband isolated measurements on the primary side of off-line designs. The switching waveforms on more recent off-line switching power supplies have transition times in the nanosecond range requiring 100+ MHz measurement performance.The big advantage they have over using a high voltage differential probe is an essentially infinite common mode rejection ratio.Quote from: Njk on February 01, 2023, 11:23:46 pmIt has been done at various times. TheTektronix A6902is a good example which is fully documented, and there aremodern faster probes.

author: Bud
author_rank: Super Contributor
timestamp: February 03, 2023, 12:16:42 am
content: Quote from: jonpaul on February 01, 2023, 09:40:49 pmFolks in the other thread must be getting a heart attack caused by your posthttps://www.eevblog.com/forum/chat/do-you-guys-use-an-isolation-transformer-for-your-labworkbench/msg4675405/#msg4675405

author: bdunham7
author_rank: Super Contributor
timestamp: February 03, 2023, 12:30:16 am
content: Quote from: David Hess on February 03, 2023, 12:15:29 amYes, something like my TPS2024 has better real performance than even my A6909 isolator, let alone modern discount differential probes. Here is a shot of me measuring the output of the Bodnar pulser using a P6139 (not properly compensated, but it matters very little) with just my fumbly hands and a regular ground lead--I didn't bother putting the ground collar thingy on it.

author: David Hess
author_rank: Super Contributor
timestamp: February 03, 2023, 12:56:13 am
content: Quote from: bdunham7 on February 03, 2023, 12:30:16 amTektronix took advantage of their CCD based sampling technology to make a small and low cost sampling front end for that series of DSOs. Once the high speed sampling is complete, the analog samples are convert at low speed and the digital data is transferred across the isolation barrier.An all digital design would have required a high speed digitizer and pile of fast SRAMs for each channel making it much more expensive. Tektronix had DSOs like that, but they were not portable and never had isolated channels.

author: mawyatt
author_rank: Super Contributor
timestamp: February 03, 2023, 03:18:48 am
content: Quote from: David Hess on February 03, 2023, 12:56:13 amTek also used their custom CCD semiconductor fab process to produce some of the better CCD imaging chips back then.Best,

author: tautech
author_rank: Super Contributor
timestamp: February 03, 2023, 09:23:38 am
content: Found some time to play.....All following square wave/step response checks are from one of Leo Bodnar's fine 10 MHz pulsers and in this one's case, a 30ps pulser.First, the pulser alone into internal 50 Ohm input attenuation in SDS6204A:(used for later reference trace)Next is with Siglents SAP1000 active probe on Ch1 with ground spring and tip connected to the back side of the BNC pads on Leo's pulser where we can plainly see even its 1.2pF input capacitance can impact on the fidelity of the pulse.So with some simple trickery with a reference trace captured as a fidelity reference (leftmost) and pulser on ch4 and active probe on ch1 the propagation delays from the different input paths have all 3 traces nicely staggered for us to easily compare them all.Edges: Reference trace then Ch4 50 Ohm input to Bodnar pulser and last, ch1 Siglent SAP1000 active probe.Where to from here ?Well only a 1 GHz active probe has been used thus far and I have 3 passive probe's step responses yet to check, Siglent 500 MHz SP5050A that comes with SDS6204A, Pintek 500 MHz CP-3501R/pro and Pintek 600 MHz CP-3601R.This is where things get interesting as we must compare each one by one using the Bodnar pulser terminated into 50 Ohms with the probe tip to BNC adapter for the connection and the probe step response is just what it is....providing LF and HF compensation has been set correctly.Here we have a teaser with a couple of NIB probes, freshly LF compensated and compared to the reference trace which indicates HF compensation needs also be checked.To be continued......

author: jonpaul
author_rank: Super Contributor
timestamp: February 03, 2023, 10:01:57 am
content: Rebonjour à tous! Bravo pour Tautron, Very fine work on the Leo B 40 ps.Years ago we posted some similar results on Tektronix 7104/7A29, 7B10, 7B15, and 2467B, and digital Yokogawa DL7440. ("show us your square wave"?) We tested sans probes, our trusty Leo B 40 ps direct to scope 50 Ohms, with a few setup improvements:1/Pulser at 10 MHz rate, Fine transient response shown at faster sweep rates, to the fastest on each scope.The Tektronix 7104 1 Ghz fastest analog scope is amazing.....2/ trim of scope ( and plug-in) vertical response can be optimized for best BW or cleanest transients response. BUT Not both! Our work in digital audio transmission and wideband transformers required best transients response. the modern Chinese scopes preffered to optimize first BW specs, not transient abberation.We have spent many happy hours tweaking fast scope verticale amps for best transients..many interacting trims, some are fragile tiny ceramic disc trimmers, or a few turns nano Hy coils, not for the faint of heart...3/Observéd Transient abberation is affected by the pulser and scope VSWR, due to reflections.Our old trick is to insert a wideband 20 db passive attenuator between the pulser and the scopes input.We reccomend Mini-Circuits HAT-20 BNC in-line. Many Ghz band. The results always show some improvement.Textmatic.....LeoB 40 pS>>>HAT-20 attn>>Scope 50 Ohm input.https://www.minicircuits.com/WebStore/dashboard.html?model=HAT-20%2BSo, have an Absolutely fantastic day!Bon SoiréeJon

author: bdunham7
author_rank: Super Contributor
timestamp: February 03, 2023, 04:53:56 pm
content: Quote from: tautech on February 03, 2023, 09:23:38 amVery nice! Since you have the equipment to show off, perhaps you could demonstrate the effect of probe loading on the actual signal by connecting a passive probe to the pulser as you've shown and then probing the backside with your active probe. The 1.2pF of the active probe did have a slight effect on the rise time (~30ps or so) of the direct signal, but that was pretty subtle.

author: tautech
author_rank: Super Contributor
timestamp: February 03, 2023, 08:08:25 pm
content: Quote from: jonpaul on February 03, 2023, 10:01:57 amThis one is actually 28ps according to the screenshot provided with it from Leo.QuoteYes I know these tricks too but......to not get too complex and confuse the readers we have not used one but that is coming.For now when we need external termination of the Bodnar pulser a Tek 1x 50 Ohm BNC feedthrough has been used but you've only seen its effects in the last screenshot and it's loaded with 2 passive probes.IIRC Tek rated these feedthrough's to 1 GHz and I also have a 10x version that we will later use as a pad but higher input sensitivities will be needed of course but we save this for a later installment only using the 10x pad so to reduce the chance of reader confusion.For interest I got a new Pintek 1x 50 Ohm BNC feedthrough a couple years back and the VNA indicates it's better than these great old Tek terminations so we might also be comparing how it and the Tek affect the step response waveform.http://www.pintek.com.tw/customer/pintek/upload/PL-50pro-DM.pdfQuote from: bdunham7 on February 03, 2023, 04:53:56 pmYes but worthy of demonstrating as the old adage;every measurement changes the measurement, is very valid when we examine results closely.As time permits we certainly will look at many more things in detail and maybe even differential probes of which I only carry 25 MHz models to display although their rise times are slow they are quite adequate for many tasks......then there's current probes too which no power engineer shouldn't be without for which a Tek P6021 with passive termination is probably still the best bang for buck if you can find a good one after how many decades in production ?Like Jon I have the 6021 and 6022 < both highly valued pieces of kit.

author: Njk
author_rank: Frequent Contributor
timestamp: February 04, 2023, 02:52:57 am
content: Quote from: David Hess on February 03, 2023, 12:15:29 amThanks for the link, it was interesting to see how they did it back in eighties in a pure analog way. Indeed, the isolation not something new but to-day it can be done in a number of different ways, because digital semiconductor technology is much more advanced now. For instance, google for isolated ADC or something like that. And it does not look like the price for T&M equipment is closely related to the cost of its internal components (RAM, etc). Some related discussions on this forum as well. What is remarkable, however, is that a battery, i.e., a thing that uses kilograms of precious raw materials, is still much more economical solution.

author: jonpaul
author_rank: Super Contributor
timestamp: February 04, 2023, 04:26:31 am
content: NJK, Tautech, Bdunham7:Found my 2019 Tektronix 7104/&A29/LeoB 40 pS shots with Mini Ckts 20 db 50 Ohm atten.After selection of 7A29 and transient response adjustment both 7A29 and 7104, perhaps the best I can do.Your thoughts appreciated!Lower pix BNC inline atten and 50 Ohm term collection.Vive l'ANALOG! Vive TEKTRONIX!Bon week-end!Jon

author: jonpaul
author_rank: Super Contributor
timestamp: February 05, 2023, 02:59:48 pm
content: Rebonjour,New scope shots of Leo B 40 pS with/sans Mini Ckts -20 db to the reduce reflected energy from scope t pulser due to VSWR or Zo mismatch.Yokogawa DL7440 500 MHz BW, FS = equv 100 G/sec, sweep at 1 nS/divupper LeoB40>>Scope 50 Ohmlower: LeoB40>>Mini Ckts HAT-20 atten>scope 50 Ohm inputYour thoughts?Jon

author: David Hess
author_rank: Super Contributor
timestamp: February 05, 2023, 06:58:15 pm
content: Quote from: tautech on February 03, 2023, 08:08:25 pmWhen using faster ones the limiting factor tends to be common mode rejection, so there may be no benefit to a higher bandwidth differential probe.

author: tautech
author_rank: Super Contributor
timestamp: February 05, 2023, 07:18:19 pm
content: Quote from: David Hess on February 05, 2023, 06:58:15 pmOf course unless you need that resolution.I was heading towards eventually demonstrating propagation delays with various probing techniques where I may need to revert to 100 MHz rated probes to get somewhere nearer the good ol' DP-25 differential probes we carry.Thanks for the poke and hopefully can provide some more pretty pics soon.

author: jonpaul
author_rank: Super Contributor
timestamp: February 05, 2023, 07:45:45 pm
content: Differential probes are by definition active, and with rare exceptions like P6046 TEK, have limited BW.They have their place esp the HV 4kV CATIII but are not useful in high BW work.Jon

author: BillyO
author_rank: Super Contributor
timestamp: February 05, 2023, 10:57:13 pm
content: Quote from: jonpaul on February 05, 2023, 02:59:48 pmThere seems to be a reasonable reduction in ringing.

author: David Hess
author_rank: Super Contributor
timestamp: February 06, 2023, 12:39:41 am
content: Quote from: jonpaul on February 05, 2023, 07:45:45 pmThe Tektronix P6046 was particularly useful beyond its bandwidth rating because it had useful common mode rejection beyond its bandwidth.

author: jonpaul
author_rank: Super Contributor
timestamp: February 06, 2023, 01:06:46 am
content: Rebonjour, David, BillO: Mille mercis pour tes idées et feedbacks.1/ We used P6046 in 1971..1975 with the Sequerra Tuner at 10.7 and 100 MHz. Entire tuner RF/IF was full differential.https://hometheaterreview.com/sequerra-model-1-fm-tuner-reviewed/2/ We found P6046 was delicate mechanically, electrically and has a thick cable. We made special PCB and test fixtures to mate to the probes inputs.https://w140.com/tekwiki/wiki/P60463/ The max voltage range +/- 25V is critical as even a sub uSec transient or static can blow the sensitive probe inputs. Very hard to repair!"Use the shorting plugs on the tips when not in use: Ground the probe! Seriously. Sticker the probe "Ground Me!" ."We always protect the tips with the 10X attn head. That head increases the range to +/- 250V.4/ As most of our work high speed afterwards was single ended, thus CMRR was not an issue.5/ All questions re the 120/230V PSU connections, testing, iuse of ground lead are in the manual:https://w140.com/Tek_P6046_Differential_Probe-Operation_Manual.pdf6/ By analyzing the measurement requirement and system block, we seldom find a need for the differential probes, high speed or HV, even though we have both.99%of times we use single ended V and current probes.Being retired, my work is reduced to SMPS/Electronic Ballast (use mains isolation transformer) digital audio transmission and magnetics, eg AES/EBU/SP/DIF, baud rate to 24.576 MHz >> BW ! 125 MHz.Hope this is of interest,Have an ABSOLUTELY FANTASTIC day!JonPS: for WB fast work, we use just a coax to BNC to make a Zo probe or TEK Zo probe P6136.10X: Of all the TEK 10X probes accumulated since 1968 (!) the most useful, robust and practical (tips, ground return lead, BW, aberration) we use is P6137, way better than the smaller or larger TEK series.

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2023, 08:55:17 am
content: Quote from: tautech on February 03, 2023, 09:23:38 amContinuingBy trial and error the best feed through was found from 3 for the lowest ringing to terminate the Bodnar pulser into for testing HF probe step response. The Tek 1x was the winner with the least overshoot to initially do the HF compensation to a direct BNC connection from the pulser.Pulser, feedthrough's, Siglent PS3050A 10x and Pintek CP-3501R 10x probeSAP1000 and Pintek CP-3601R 10x probe3 passive probes were checked against the Ref waveform captured from the Bodnar pulser into Ch4 input.Each of these required HF compensation (see above screenshot) for which I used the Bodnar 10 MHz pulser whereas all probe pamphlet instructions state 1 MHz should be used and peaks (overshoot) should be within or no higher than max amplitude.However I chose on this occasion to best replicate the Ref waveform with all HF adjustments and the results are as follows.Then a check with the SAP1000 1 GHz active probe on the rear of the pulser BNC with it connected to the termination to check signal fidelity was near to our previously saved Reference waveform. Near enough is the verdict and gives us an indicative risetime of some 340ps to compare passive probe performance against roughly 80ps slower than the direct BNC connection.SAP1000Siglent SP3050A 500 MHz 10x sense probe proved the most difficult to perform the HF compensation upon for the following screenshot.Pintek CP-3601R 600 MHz 10x probePintek CP-3501R 500 MHz 10x probe.The surprise is the Siglent SP3050A while not providing the best step response did provide what appears to be the slightly better rise times.Next up are some other probe checks, PP215, a SP2030A we have lying about and a couple more Pintek 10x sense probes, CP3351R and CP3101R and while at it we should also test 100x CP3308R 2kV and 1000x HVP-08 8kV probes.

author: jonpaul
author_rank: Super Contributor
timestamp: February 06, 2023, 10:48:02 am
content: Hello, very fine but.....1/ Your shots Time/div much too slow to see fine structure of transient response and aberration.Use a 1 ns or faster /div. on DL7440 Yokogawa, or TEK 7904/7104/7B10/7B15.Unsure what the Sigeilnt scopes are capable of.2/ There are Many poorly made or old 50 Ohm terms/feedthrough are about. Check the BW and Zo of your terms on a wideband network analyzer or impedance analyzer at least 1 Ghz.We found the Mini Circuits and old EGG are the best, most robust and widest BW.3/ No need for any feedthrough in scope testing if scope of plugin has a50 Ohm inut.That is better than an external feedthrough term.Enjoy,Jon

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2023, 06:52:37 pm
content: Quote from: jonpaul on February 06, 2023, 10:48:02 amPlease see and understand first 2 screenshots in this earlier post:https://www.eevblog.com/forum/testgear/probe-into-probes-whats-up/msg4678768/#msg4678768We require the Bodnar pulser to be externally terminated into 50 Ohms to provide a 25 Ohm source for probe HF calibration, risetime and step response tests against a previously saved reference trace that used the scopes internal 50 Ohm input.We are using a 2 GHz rated 4ch DSO and for you the EU link:https://www.siglenteu.com/digital-oscilloscopes/sds6000a/Fastest timebase is 100ps/div

author: jonpaul
author_rank: Super Contributor
timestamp: February 06, 2023, 07:33:51 pm
content: Tautech:Many thanks, good link for the scope.still do not see any shots at fast sweep, only the 10 nS/div, can you show shots like those references with fine detail at 1 nS..200 pS/div?All my work was at 50 Ohms, no probes jut the pulser>>scope at 50 Ohms internal.Thus a bit different than your very interesting probe tests.Be good to do a check of feedthru 50 Ohm BNC/SMA terms, of various brands and ages: LeoB>>50 Ohm Term>>1 M scope to see the cheges in term VSWR at fast edge.Enjoy,Jon

author: Bud
author_rank: Super Contributor
timestamp: February 06, 2023, 09:39:03 pm
content: Quote from: jonpaul on February 06, 2023, 01:06:46 amHow important the ground lead length on P6046 is for signal integrity? Same as for a single ended probe or is it more for electrical safety of the input FETs?

author: jonpaul
author_rank: Super Contributor
timestamp: February 06, 2023, 09:52:22 pm
content: bud, as P6046 is differential, indeed ground lead legnth is not as,critical as in single ended probes.However the HF CMRR rolloff limit the effectiveness thus the ground clip is,useful.Since the FET front end has a CM and DM voltage limit, the CM input 1 r input 2 to ground voltage can be easier exceeded if no ground or a,long ground,lead with attendant high inductance is present.We always used the standard ground leadSo not as much for safety (only low,V use of these probes) but to protect the ET inputs.Jon

author: Bud
author_rank: Super Contributor
timestamp: February 06, 2023, 10:20:19 pm
content: Thanks Jon. The standard ground lead you mean the one you snap to the ground clip on the probe casing? (Not on input 1 or 2 tip ground)

author: tautech
author_rank: Super Contributor
timestamp: February 06, 2023, 11:24:56 pm
content: Bud, this is P6046:

author: Bud
author_rank: Super Contributor
timestamp: February 07, 2023, 12:31:32 am
content: I know what P6046 is, I have oneThere is a short ground post on the other side of the probe head, to which you snap a ground lead of a required length. This is what i was asking about.

author: tautech
author_rank: Super Contributor
timestamp: February 07, 2023, 12:54:37 am
content: Quote from: Bud on February 07, 2023, 12:31:32 amGotcha.Yep our P6021 and 6022 have those too.

author: Bud
author_rank: Super Contributor
timestamp: February 07, 2023, 12:54:47 am
content: There it is

author: jonpaul
author_rank: Super Contributor
timestamp: February 07, 2023, 12:55:58 am
content: yes the ground terminal on the opposite face of the probe body which accepts a standard Tektronix ground lead.j

author: Bud
author_rank: Super Contributor
timestamp: February 07, 2023, 01:11:34 am
content: Right, so I am wondering if it makes sense to use the ground ring of the tip , instead of the long ground lead.I guess there is a merit to do this if you use the probe in single ended mode with the second tip shorted because in this case return path goes through it. But for differential measurements I am not sure if connecting ground to tips' rings vs the standard ground lead may make a difference from signal integrity perspective.

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2023, 08:12:58 am
content: Quote from: jonpaul on February 06, 2023, 07:33:51 pmOkay, lets examine more closely the Siglent 500 MHz 10x SP3050A response from the Bodnar > Tek 1:1 50 Ohm feedthrough in the 2nd pic in my earlier post.Looking faster and with some Vertical zoom and Horizontal fixed position.Right down to 500ps/div and 20mV/div, equivalent of 2mV/div with 1x inputs.QuoteI only have BNC feedthroughs, most 1:1 and just one Tek 10:1, the brown one in the earlier photos.I'm instead inclined to do a Through on the VNA where I can push them to 8+ GHz although I only have a SMA Cal kit so can't Cal beyond the N-BNC adapters and I don't possess any high quality BNC cables, only off the shelf 1 GHz rated variety. If I place the 50 Ohm terminations on Port 1 for a S11 SWR and a S21 Through measurements we should have enough to be comfortable in selecting the best and worst for comparing probe response with each of them....will do later if we find time.

author: jonpaul
author_rank: Super Contributor
timestamp: February 08, 2023, 12:44:05 pm
content: If the scope has an internal 50 Ohm input, why do you eed any extenal feedthru?All of our tests on DL7440, 7104, 78904, 7A29 use only the 50 Ohm inout.Pluse Gen>>50 Ohm -20 db attn>>scope 50 Ohms.Unless you test a probe , just test the scope with no probes.Jon

author: BillyO
author_rank: Super Contributor
timestamp: February 08, 2023, 05:48:34 pm
content: Quote from: jonpaul on February 08, 2023, 12:44:05 pmHe is demonstrating the probes.

author: tautech
author_rank: Super Contributor
timestamp: February 08, 2023, 07:44:35 pm
content: Quote from: jonpaul on February 08, 2023, 12:44:05 pmDone 1yr ago:https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg4032745/#msg4032745

author: tautech
author_rank: Super Contributor
timestamp: February 09, 2023, 08:04:52 am
content: As we were examining probe step response the SWR of 50 Ohm feed through terminations in my probe tests was seen to influence overshoot and a Tek 1:1 termination was selected for tests only in that it seemed to have the least influence.However this should be properly quantified and as we have the toolswhy not put all 4 onto our SNA5000A 4 port VNA and sweep them to 2 GHz for a SWR check.Note the SWR measurements top right at 1 GHz and the 3 different vertical scales used.

author: jonpaul
author_rank: Super Contributor
timestamp: February 09, 2023, 01:03:46 pm
content: Rebonjour a tous....accumulated from Ham Radio fleas, silent key estates, epay.The P6046 TEK diff probe collection: Unused for 20 years, just unearthed.2 probes 2 amps/PSU, All accessories, incl X10 attn and shorting tips (large gray tips)The VERY rare probe body housings and special probe CAL housing ( from the late and great Deane KIDD?).Works fine after a bit of lube on the amp zero controlAMAZING INSTRUMENT Very sensitive very stable.Issues: Needed fooling with zero DC adj pot on amps cleaning of PSU, amps, probe bodies (iso alc)Case foam going badHope to test CMRR and NM gain vs freq on HP4195A 100k...500 MHz in 50 Ohm environmentSeeking the original printed manual, can offer swaps for other orig TEK printed manuals.Your feedback appreciated!Bon Soiree!Jon