#338

[@MrCarlsonsLab]

Nice to see a new video from you Alan. Great stuff!

[@w2aew]

Thank you Paul - means a lot coming from you!

[@emailuser3869]

Mr. Carlson, are you a HAM?

[@allenlutins]

I've been measuring RF in an EMI lab for a decade and a half, and no one's ever given me a heads-up about this particular concern. Thank you!

[@edinfific2576]

That's weird, because they definitely should have if it's a lab of any repute. Maybe they assumed you knew enough about the job.

[@allenlutins]

@@edinfific2576 I'd say we have an excellent reputation, and that it's well deserved. The problem is that EMI is a very broad and complex field, and little formal education is available for techs like myself. I learn something new every day - usually on the job - but sometimes from fine folks like w2aew :)

[@edinfific2576]

@@allenlutins You're right. I had once worked for Maxim Integrated, great company to work for, nice people. I was a technician in a lab, mainly making and testing DC-DC converter circuits aparently for demo kits and purposes, and an engineer would give me the schematic for the circuit needed. It took me a few weeks to realize that the other technicians in the lab who had been working there for quite a few years lacked even the basic knowledge in some areas. But they knew enough to get the job done. And if you are sufficiently interested in electronics, your knowledge and understanding can approach or even exceed the level of an engineer, at least in some areas. It is an ever-pursuit of knowledge and it is rewarding when you are able to analyze or build your own circuits, and you become like a master in your field and can command a higher pay and respect. I wish you success.

[@sollykhan2385]

great video thank you for posting, please post more great content 🙂

[@JB-20]

I'm late but always love watching your videos.

[@billyhart3299]

I gotta say, man, I owe a lot of my success in electronics to your channel, and this is a great video. Thank you.

[@philso7872]

Connecting a second probe of the same type in parallel while monitoring the waveform sensed by the first probe will show if the first probe was affecting the circuit. The frequency and amplitude of some parts of the signal will change as the second probe is connected.

[@w2aew]

Excellent advice.

[@supernumex]

Wow, great tip!

[@johnpeterson7264]

Excellent video. Actually - an excellent series of videos on scopes. Actually - one of the BEST channels on YOuTube !

[@dkabell]

Great to see another informative, focused vid professionally delivered. I always look forward to your videos.

[@segrus]

0 dislikes, best videos and best professional! Thank you!

[@edinfific2576]

I like that you don't have any "music" in your videos because it would only be a nuisance and most people also have a very terrible choice of "music" and allow it to drown their voice (fade in and out and level issues). I love your good, simple, short, to-the-point, logical, rational and knowledgeable explanations. Just keep the format, you don't need to change a thing, I can't think of ways to make your videos better. P.S.: I just noticed I wasn't subscribed, which I have corrected immediately. 😁 Even so, KZbin recommended this video to me within 8 hours of your posting. 😀

[@kenwezeman7827]

I agree with everything you said (except I am already subscribed.)

[@andrewferg8737]

Always an education. I've never been very confident in my ability to accurately measure RF circuits with my oscilloscope. This video may help. Thanks again.

[@sasines]

Always great advice Alan. Wish you had been one of my professors when I was in college. You have an outstanding way of making the most complex issues understandable. 73!

[@electron_]

Great video as always! As a electronic engineer whenever I have RF circuit I am checking my probe nearby oscillatora and after buffer ( amplifier) if there is frequency of difference between those two measurements, it is always good idea to find active probe. Thanks for great advices.

[@edinfific2576]

I was aware of this but didn't pay much attention to it. We tend to think of instruments as if they're outsiders just observing a circuit, while in reality they become a component of the circuit being measured and influence the behavior of the circuit just like any other component of its characteristics, whether it's the resistance, capacitance, inductance, impedance or even a non-linear characteristic if the instrument's input contains non-linear elements (diodes at the input, for example). I had an RC circuit with a 10k resistor and a 47pF capacitor, and even the 10× (or 10:1) probe has between 10 and 20pF, enough to present up to 40% of the circuit's own capacitance. But now I have a 100× (100:1) high-voltage probe (Testec TT - HV 250, 2.5kV), rated for up to 300MHz and has "only" 4pF input capacitance, but even so it is almost 9% of the circuit's capacitance and its effect can be seen, and this is at only 100kHz signal frequency (but in an edge detection circuit).

[@rabbibacongrease88]

I wonder how many customers received equipment that was misaligned due to the technician's lack of awareness of this subject? Great video as usual.

[@kevinmccool3719]

This explains why they had so many unexplained weird crashes with the equipment sold, all of it needs to be recalled. 😂😂🤣😃

[@McTroyd]

Recently heard the rerun of your interview on the Amp Hour podcast. Subscribed for years, but I had no idea you were a Tektronix engineer! That's so cool. Thanks for all the informative videos!

[@w2aew]

Just a field apps engineer, not one of the wizards at the factory!

[@McTroyd]

@@w2aew I'd argue that's even better. I know from my own experience dealing with customers that being in the field requires a lot of adapting and quick thinking.

[@herbertsusmann986]

Good heads up on capacitive loading. Even 1pF from that FET probe can be enough to throw off a frequency measurement if the probing is done at the wrong point in the circuit. Gotta make sure you probe at the output of a buffer amp or similar and not at the actual oscillator crystal terminals.

[@EngineeringVignettes]

It's the Uncertainty Principle - Scope probe edition. :) As always, stellar advice! Cheers,

[@coffeecuppepsi]

Awesome I love getting notifications from this channel

[@MrBanzoid]

Very informative video Alan. Thanks.

[@hedleyfurio]

Another Gem - many thanks . You really have found your calling in life.

[@SeanBZA]

Yes the probe can often be worse for the circuit than a terminated 50R load, as at least that acts like a transmission line and can be compensated for. The reason why a lot of the more expensive equipment puts in a 20 dB pad and a test point, so that they can simply connect a coax cable and measure without disturbing the circuit, and even if it is left open circuit after manufacture the attenuation will not be a worry with any reflection. Saw that on an old RF distribution amplifier, where there is both an input and output test connection, with a selectable 20 or 34 dB loss to them, so you can just put a coax cable on to measure in circuit. Figured out why it was not working, the topswitch power supply has a popped 10uF 400V capacitor, and the remains of a 8 pin topswitch next to it. But then again, analogue TV is still running, only 11 years after the rest of the planet switched it all off. Might be turned off fully by 2025.

[@JacquesConradie]

Thanks Alan, I've learnt something new today! Keep it coming please !

[@Justplast]

good to see you again A1 as always.

[@montygore]

Great video. Very Informative.

[@bblod4896]

Great short class Alan, thank you and 73s.

[@DhammaChakkhu921]

Thank you Alan.

[@cmuller1441]

Active probes are great but very expensive. Maybe it could be a good idea to make a small diy circuit that goes in front of the 10x probe to buffer the signal to reduce the capacitance. Even if the final bandwidth is not 1GHz, it doesn't matter because most amateurs don't have a scope that goes that high. I wonder if just a simple emitter follower powered by a tiny lipo battery (to keep it light) is enough to improve the situation.

[@Gengh13]

1k likes and 0 dislikes, an excellent indicator of a quality video.

[@DonDegidio]

Hi Alan, Another great video tutorial. I had known that the scope probe could load a circuit, but you have shown how heavily it can load the circuit at selected points. Keep them coming. Always enjoy learning from your videos. You and the family stay safe. 73 WJ3U

[@W1RMD]

Thanks for another great video!

[@researchandbuild1751]

I ran i to this problem measuring the output of my diy 144mhz amplifier..solved it with a resistor circuit

[@copernicofelinis]

How about a follow-up video on the use of Bob Pease's high impedance probe published on EDN Jan 19, 1989 (p. 159)? Two FETs and two BJTs and you get a front end with 0.29 pF and 100 Gohm.

[@w2aew]

I’ll have to dig up that article.

[@jenniferwhitewolf3784]

I sure miss Pease Porridge.. He left a huge legacy of wisdom, but I am sure there was still much to come... Rest In Peace Bob!

[@jenniferwhitewolf3784]

That issue is not on the EDN Archive. I would love to see that article.

[@mmaranta785]

@@jenniferwhitewolf3784 I used to email Bob Pease a lot and he would answer. Very knowledgeable and cool dude.

[@w2aew]

@@jenniferwhitewolf3784 There is an image from the article in this EEVblog forum post: www.eevblog.com/forum/testgear/high-impedance-low-capacitance-scope-probe-for-open-drain-meausrements/msg2318136/?PHPSESSID=okesekntsqhrq05v3d8abbnsk3#msg2318136

[@FireandFrostHVAC]

Excellent video, thank you.

[@R2AUK]

Thanks again for sharing! A very nice video 👍❤️

[@valdirdeaguiarlima7241]

Always excellent contents! Would give you a thousand thumbs up, if possible.

[@radiotvrepair1059]

Thanks for this vedio

[@andrewverran3498]

Didnt understand a thing..but it was a thumbs up as the problem was with me..

[@1828fernando]

Great video. Thank you!!!

[@TKomoski]

Always the loading things that are always forgotten

[@PapasDino]

Great! I got to be #500 thumbs up! ;-) Great video Alan and I'd like to see you take a look at Pease's article and see what you might be able to do for us as another commenter mentioned. 73 - Dino KLØS

[@EnergySeeker]

nice video i want to ask you when i measure DC capacitors signal with my 100x scope lead do i need to connect the ground ? because when i connect it it short out the output , and if i make the scope without ground plug i get 120v signal on the dc output :( what should i do ? thanks

[@w2aew]

You should always connect ground, but always make sure that you connect it to ground in your circuit! A scope probe (and scope) are generally NOT floating like a DMM, so you ALWAYS have to take care about ground. Floating the scope (removing the ground pin) is unsafe. There are specialized oscilloscopes with isolated inputs if you need to make measurements where there is no convenient ground, or use a differential probe.

[@EnergySeeker]

@@w2aewthank you for answering that fast

[@mathiasjapri]

Glad new videos is up again, can you do a tutorial how to verify real 2sk170? thanks

[@andymouse]

Great tutorial cheers.

[@iw0hex]

Very nice video, thanks for sharing. 73s Pasquale IW0HEX

[@mehmetcemarmagan2005]

Mind that our eye resolutionitive resistance and capacitance in the time and also can we measure our brain cell characteristics with NanoVna? I want to be very certain about my calculations. Cheers btw thanks for your knowledge and time.

[@buffplums]

Excellent demo mate cheers!

[@Fireman9143]

Is that what I see when I touch the tip of the probe and the ground with one hand? I figured my body was acting like an antenna with RFI.

[@w2aew]

Yes, your acting as an antenna. Often you see 50/60Hz power line pickup, or even RF signals.

[@cactusheart9632]

Side question: how are you able to buy bare die in presumably low volumes? I only know how to do that for the company I'm working for but not for myself. Any particular suppliers you'd recommend for low volume purchases?

[@bayanicruz8914]

Gud day sir..may i ask what is the purpose of using signal generator in vhf base radio which is out of freq or whag we called not in center freq.. tnx..

[@AhmedIsmail-sw6so]

i need video in design helical normal mode antenna for 410Mhz and test it in your lab

[@silasmarner7586]

GGB had an active probe which effectively cancelled the capacitive loading and greatly improved bandwidth. It was a bit touchy and very spendy tho.

[@silasmarner7586]

Gee whiz it must've been a few years since I last looked. They've got some smokin' hot active probes but then again so does Tek.

[@gangaskumar1922]

Can you please explain how to extract the parasitic capacitance of an oscilloscope, the probe capacitance is 3.9pF.

[@w2aew]

I'm not sure what you are asking for? The 3.9pF probe capacitance *is* the parasitic capacitance that the probe adds to the measurement point of your circuit.

[@RixtronixLAB]

Nice info, where can I buy active FET probes ? thanks :)

[@w2aew]

The major scope manufacturers make them, but are specific to their scopes, and are sometimes only for certain models. There are some 3rd party ones that work with any scope, such as www.digikey.com/en/products/detail/cal-test-electronics/CT4121/6111354 Most will require a 50 ohm termination.

[@nicolaswannen1743]

I am wondering how do you get such clean waveforms on your scope ? At my bench everything looks so noisy...

[@w2aew]

Keep your probe's ground leads as short as possible.

[@jstro-hobbytech]

Hey man. I have a tek and rigol scope and ive been through 6 rigol passive probes 1x-10x while my ancient tek probes at 1x are awesome. Can i buy a set of tex passive probes and work with my mso5354? Id sell it if i hadn't paid so much for the logic probe package. I live in a place where there's no market for one anyway.

[@w2aew]

Many Tek passive probes will work with that scope, such as P6139, P2221, TPP0200, etc.

[@jstro-hobbytech]

@@w2aew awesome. Thank you

[@SongSeeker7]

When you probed with the 8pF probe I'm trying to estimate the circuit capacitance as 8 / ((7.9976/7.9974)^2 - 1) or about 160nF which seems rather large for the xtal. Im missing something?

[@w2aew]

Don't think that formula applies, since in this circuit, an infinite capacitance in this location would only change the operating frequency by several kHz. See the G3UUR method in the linked video.

[@TheRetiredtech]

so where did you get those probe grounds?

[@w2aew]

They came as accessories with the probes.

[@waynegram8907]

How would you know if your probes capacitance value is changing or affecting the circuit you're measuring? without having other types of Oscilloscopes that support other passive probe capacitance values and active probe to compared to the electronic technician wouldn't know what the reference is or know there is a problem unless you had other oscilloscopes that support different probe capacitance and active probe to know if the probe capacitance value is loading the circuit under test. I personally would just think it was considered normal using a 5pf to 10pf probe without knowing it was loading capacitance on the circuit under test.

[@justovision]

He demonstrated that. He's measuring in two places and just observing the difference. The output of the circuit is probably able to accept a load or if not would still make a baseline for comparison.

[@waynegram8907]

@@justovision But most tech bench when working at a company don't provide oscilloscopes that SUPPORT different probe capacitance and active probe so you would have to have various probe capacitance to compare the measure Test points against.

[@1900OP]

I first figured it out when I made a high frequency oscillator, I used to find the signal on a commercial radio, when I unplugged the probe from the circuit the frequency changed. The solution was to add an emitter follower as buffer, so the probe capacitance have a much lower impact on the frequency if I put it after the buffer. Of course, if you didn't encounter problems resulting from probing, you don't need to know this thing, and as you can see in the video the frequency of his oscillator changes very little (in comparison to my LC oscillator) because it's a crystal oscillator.

[@w2aew]

As "Phil so" stated above, simply connect a 2nd probe the the same point in your circuit. If the response on the scope changes, then you know that your probe loading is having an effect, even for the first probe alone.

[@waynegram8907]

@@w2aew Right that is my main point is you would have to have different probe capacitance and the Oscilloscopes that SUPPORT the probe capacitance and active probe to compared against. Most Oscilloscopes don't support different probe capacitance or able to use an active probe.

[@tamaseduard5145]

👍👍💖🙏💖👍👍

[@mmaranta785]

If you are measuring a TTL digital circuit, and the probe is connected to circuit, and you connect probe to scope then unplug from scope, will that affect the circuit?

[@w2aew]

It shouldn't affect it much when using 10x probes.

[@sammin5764]

🌷🧡🌷🌟🌟🌟🌟🌟

[@jdmccorful]

Nice work!