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Re: Testing Scope Probes

 

By sheer chance I came across this amazing little vintage film pretty much precisely on the subject under discussion here. It's a great refresher for those of us who don't delve into this topic on a frequent enough basis to be thoroughly familiar with the principles involved:



These old films are the *best* in my view.
Re: Fume extractor recommendation

 

If I have to remind everyone, he's soldering in a garage in California! That door does open.

He could also move his soldering station onto a rolling cart and add in an extension cord. Push that unit out to lift some circuit board pads, dodge the rosin smoke, and then roll back in.

I'm pretty sure Steve Wozniak and his buddies did lots of Apple 1 soldering in a San Jose garage, and he's fine. If I had his money, I would burn mine.. ??
Re: Testing Scope Probes

 

In case there's anyone else still confused about tip capacitance vs frequency, I've again posted up the Rp and Xp plot from Tektronix for one of their old x10 scope probes.
If you look at the Xp trace, the downward slope isn't a perfect straight line. There's a knee in it at about 25MHz if you look along the line. The slope is less above this point. This means the Cp (parallel capacitance at the tip) is falling at frequencies above about 25MHz in this case. If the capacitance was the same at all frequencies the slope would be constant. It clearly isn't constant.
Often, the tip capacitance Cp falls to about 60-70% of the capacitance it shows at lower frequencies.
Re: HP 427A no DC offset adj. pot

 

Beautiful work David. I¡¯ve downloaded it and will print it out shortly (I prefer paper). I¡¯ll also post a link to it in the thread over at Antiqueradios. Thank you again,

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Re: WTB: 8350B extension cables

 

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Hi James,

these are the parts that I have for the HP8350.
If you are interested make me an offer.

Shipping from Canary Islands.

73, Rainer EA8DMF


Am 13.04.2024 um 06:35 schrieb James Morris (W7TXT):

I'm looking for the sweeper extension cables used for servicing plugins. The HP part numbers are:?

- 08350-60034 (64-pin centronics / 57 series / micro-ribbon cable)
- 08350-60035 (DCM 21WA4F/S with coax)

If anyone has these or equivalent, please let me know.

James W7TXT



IMG_20240413_125547.jpg
IMG_20240413_125553.jpg

Re: Fume extractor recommendation

 

I'm gonna chime in on this insanity.?
I prefer the M40A2 Field Protective Mask as it allows a left or right side can, as opposed to center mounted can. Better to get a cheek weld see what your soldering. You can also go with a tankers snorkel, or snuffleupagus. 3M half masks and acid vapour filters work exceptionally well, as I have used them while sterilizing clean rooms with Peridox (mix of hydrogen peroxide and peracetic acid strong enough to hit your throat like CS)
Oh, and Yuengling is superior. best black and tan I ever had was Guinness and yueng.
Also, fans. Who doesn't have a stockpile of fans at this point?
WTB: 8350B extension cables

 

I'm looking for the sweeper extension cables used for servicing plugins. The HP part numbers are:?

- 08350-60034 (64-pin centronics / 57 series / micro-ribbon cable)
- 08350-60035 (DCM 21WA4F/S with coax)

If anyone has these or equivalent, please let me know.

James W7TXT
Re: HP 427A no DC offset adj. pot

 

The scan of the 427A manual (00427-90008, June 1983) has been sent to Bama, KO4BB and uploaded here; /g/HP-Agilent-Keysight-equipment/files/All%20HP,%20Agilent%20and%20Keysight%20instruments%20in%20folders%20by%20part%20numbers/000%20to%20999/427A%20Multimeter

David
Re: Fume extractor recommendation

 

Cross post from EEV blog.

So, I Worked in electronics since 1950s, with lead solder 60/40, 63/37, and never used any precautions.

At 77 still going strong!

Jon window exhaust fan $25..50

4" electronic fan like Rotron, NMB with HEPA filter.

We use Hakko fume extractors.

For BeO dust, use face mask, gloves, face shield, respirator, NOT fume hood or fan



Dont worry be happy!

J
Re: Testing Scope Probes

 

On Sat, Apr 13, 2024 at 09:44 AM, Dave_G0WBX wrote:
And yes, that is very difficult at VHF and up, with "Probes", unless the transmission line / probe interface is "Very" carefully designed and laid out.? Related to that..? There has been mention of the probe tip "Capacitance" varying with frequency..? Really?

Don't you mean, the probe tip "parasitic capacitive Reactance" varies with frequency.? The actual capacitance value (in pF) itself wont vary appreciably, but is affected by the attached oscilloscope's input capacitance in a known way, as well as the effects of the probe's grounding to the circuit being probed being reactive, getting into the mix as well, likley much more significant than the effects of a probe's capacitive reactance.
Of course the shunt capacitance (Cp) is going to change (reduce) up at VHF and UHF because the bulk of the series tip capacitance is in series with a lossy transmission line. There is some shunt tip capacitance as well, but the circuit loading effect of a typical x10 scope probe can be crudely modelled as about 12pF in series with about 60 ohms resistance. This crude model holds true across about 10MHz to maybe 150MHz.
Try computing the equivalent Cp and Rp of (say) 12pF in series with about 60 ohms series resistance and do this across 10MHz through 150MHz. The Cp will fall above about 50MHz. It will stop falling at some point because of the shunt capacitance at the tip/nozzle of the probe will still be there. This capacitance is a small tip shunt capacitance and it isn't in series with the lossy transmission line.
Re: Testing Scope Probes

 

Hi..

This from the perspective of someone who has been using 'scopes and probes, both as a user (professionally and as an individual) for well over 4 decades!? (My first "real" 'scope, was a Solartron CD 711S.2, while I was still at school. It weighed nearly as much as I did, and all of 7MHz 3dB bandwidth!? It also made a great room heater.? (Remember when electricity was cheap?)

I Also was involved in servicing/repairing them (again, professionally at Tektronix UK in the past, and latterly as a hobby in recent times.)

Tek (and no doubt HP also) had an application note, detailing the relationship between system (10% to 90%) rise time and 3dB bandwidth.? (The Tek 475 manual in particular ISTR had this too) Also, how to calculate the total effective bandwidth of two cascaded systems each with a different bandwidth (probe + scope for example.)

Suffice to say, the total is always less than the lowest BW component, though if one was very much less than the other (or rest of the) part(s) of the system, it would predominate of course.

As 'scopes are "Time domain" instruments, it makes more sense to check a pulse edge rise-time and aberrations I think, as a gauge of performance, than sweeping them to find the 3dB bandwidth, though that can have some benefit as a cross check.

And yes, that is very difficult at VHF and up, with "Probes", unless the transmission line / probe interface is "Very" carefully designed and laid out.? Related to that..? There has been mention of the probe tip "Capacitance" varying with frequency..? Really?

Don't you mean, the probe tip "parasitic capacitive Reactance" varies with frequency.? The actual capacitance value (in pF) itself wont vary appreciably, but is affected by the attached oscilloscope's input capacitance in a known way, as well as the effects of the probe's grounding to the circuit being probed being reactive, getting into the mix as well, likley much more significant than the effects of a probe's capacitive reactance.

As others have already said, when probing fast digital waveforms, or RF circuits, the ground return from the probe to the circuit being probed is critical to getting a "true and representative" signal on screen vs what is actually going on in the circuit being probed.

Quite often, you will see some significant changes in other aspects of the system being probed, as you connect the probe tip. Especially in the case of digital systems where there is a "Race induced" glitch causing issues.? Probe connected, the fault goes away, and nothing untoward seen on the 'scope.? Remove the probe, and the problem returns.

Sometimes, actually inductive loading the probe ground lead will prevent the unit under test from changing behaviour, but then what you see on the 'scope screen will be distorted, but you could see any glitch signal.

As to the effects of a few mm of unterminated transmission line between a terminated source, and the probe tip.? Well, at 1GHz, the wavelength is 300mm.? A 1/4 wave is 75mm, so 5mm or so is unlikely to make much of a difference "I think."? (I don't have kit of that sort of performance these days to play with...)

But yes, place an attenuator between the sweeper source and the termination where you place the probe, to greatly reduce such effects.? Look up "VSWR reduction by attenuation".? It is a valid technique in many cases.

Even if it does, the aberrations caused are going to be at a much higher frequency (shorter time scale) than the total effective bandwidth of the overall system can cope with, so will probably for all intents and purposes be mostly negligible.

Re the Leo Bodnar pulse gen's (Obsolete now, according to his website.)

The pages state 40pS at 1Vpp into 50r, but also 2Vpp into 1MOhm. So, a likely source impedance of 50r it seems.

If you run that into a 2.2MOhm load, with a known parasitic capacitance, what sort of rise time does that likely result in? I've not worked it out, but likely to be slower than it is into 50r.

But, don't let that prevent anyone experimenting, or raising the subject on the "Time Nuts" list.? Like all such things, it's a deep rabbit hole with many twists, turns and dead-ends...

Enjoy!

73
Dave 'KBV? (Who'll be fixing wobbly tables, and doing an airport run today.? And also learnt never to trust any measuring instrument to be 100% truthful in what it is showing you!? They all lie, to a lesser or greater extent.)


--
Sent from a Micro$oft free zone:
Re: E4406A starting problem

 

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Qual l¨ªngua voc¨º fala? Estou adivinhando portugu¨ºs.

Este tipo de fonte de alimenta??o pode ser extremamente perigoso. N?o tente consert¨¢-lo a menos que saiba trabalhar com altas tens?es.

On 4/12/2024 5:11 PM, Jesse Joabe wrote:

But where do I connect??

Re: Testing Scope Probes

 

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A long time ago Tektronix made a little board for adjusting scope probes and Seeing frequency response. I think I have a couple here. ¨C Mike

?

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

?

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Kuba Ober via groups.io
Sent: Friday, April 12, 2024 4:17 AM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] Testing Scope Probes

?

Jinxie, Ultimately, the probe is supposed to measure things. If it measures things well, that¡¯s all.

?

Get a square wave going from a generator, put it through a couple of fast inverters in series, surface mount, well decoupled, on a ground plane, and measure with known good probe and the eBay probe. Not at once! Save the response traces in the scope or on a computer to compare them. Be very careful that each probe attachment is reproducible. Ideally you¡¯d solder a ground sleeve to the pcb, then slide the probe tip into it. That way the geometry will be reproducible between probe insertions.

?

If their response is very similar at all time scales, from 1s and 2Hz wave down to 100MHz square and 3ns around the edge, then that¡¯s all you care for. Then, to ensure that the low output impedance of the inverter doesn¡¯t obscure things, add a series resistance on the output, say 500R. If both probes do the same thing then too, you don¡¯t even care if the eBay deal is a fake or not. It works just as well.

?

Sure, a fake may be less durable, react more to humidity and so on, but it¡¯s really unlikely that it¡¯d have identical response yet different construction. The parasitics determine the probe response too, it¡¯s a part of the design process to make them work for the design and not against it. In practice, you could copy the geometry of the genuine probe perfectly, with all conductive parts idebtical, but unless you used the same compositions of plastic dielectrics as in the original, you¡¯d still end up with a different response - different enough to measure! Unless you got very lucky that is.

?

Measuring two probes at once from the same source is tricky. Using fast inverters as a signal source you could fabricate two machine-assembled PCBs, carefully solder the probe sleeve using a fixture so that it¡¯d be within <0.1mm from where it is meant to be on both boards. Then feed the boards from the same square source and measure probes in parallel. The probe tip should be touching a slightly enlarged pad on the output of the final inverter. This will keep the geometry much tighter than playing with BNC tees and such.

?

Cheers, Kuba

?

?

?
Re: Fume extractor recommendation

 

Fa sho!? IPA is good.? ?But Guinness is the platinum standard,? being a coronary medicinal beverage...


On Fri, Apr 12, 2024, 2:55?PM Peter Gottlieb <hpnpilot@...> wrote:
You definitely need to upscale your beer choices.


On 4/12/2024 3:47 PM, Chuck Harris wrote:
> As I recall, they both taste the same...
>
> -Chuck Harris
>
>
> On Fri, 12 Apr 2024 12:00:06 -0700 "Tom Lee" <tomlee@...>
> wrote:
>> Intermediate Power Amplifier (as opposed to a Final PA).
>>
>> Or maybe India Pale Ale. One never really knows...
>>
>> Tom
>>
>
>
>
>
>
Re: HP 427A no DC offset adj. pot

 

Good to hear David. I can¡¯t wait to download it.?


³¢±ð´Ç²Ô¡­
Re: unusual 3400a

 

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Never mind! I just realized I grabbed the wrong meter!


On 4/12/2024 11:59 AM, Gary Appel wrote:

I wanted to calibrate my 3400a RMS voltmeter, but it doesn't match any of the manuals available online. It is SN 1208A13887. On the back of the meter the DC output is from a banana jack pair, and there is provision for running the meter off +/- 35 to 55 volts. It contains a single horizontal board (and a second small board - probably an amplifier in a shielded enclosure behind the BNC input), with no plug-in boards.

Does anyone have any information on this variation of the 3400A?

Thanks,

Gary Appel

Re: Testing Scope Probes

 

On 4/11/24 16:53, jmr via groups.io wrote:
See below for my homebrew Zo probe. It really does do a good job here and agrees very closely with the direct 50R output on channel 1.
That is a complete shape match! Really good.
unusual 3400a

 

I wanted to calibrate my 3400a RMS voltmeter, but it doesn't match any of the manuals available online. It is SN 1208A13887. On the back of the meter the DC output is from a banana jack pair, and there is provision for running the meter off +/- 35 to 55 volts. It contains a single horizontal board (and a second small board - probably an amplifier in a shielded enclosure behind the BNC input), with no plug-in boards.

Does anyone have any information on this variation of the 3400A?

Thanks,

Gary Appel
Re: E4406A starting problem

 

But where do I connect??
Re: Testing Scope Probes

 

That's the fast pulse generator I mentioned I have further up the thread, the Leo Bodnar one. I bought it for TDR purposes but have never used it in anger since I've had it. Perhaps this could finally be a good use for it!
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