EEVblog

[@harbselectronicslab3551]

What a shame Jim Is gone now..........a legend in electronics

[@demef758]

For the EE students out there: this formula of BW * Tr = 0.35 is easy to deduce. Make an RC low pass filter. What is its bandwidth? BW = 1/(2πRC). If I apply a step function to the input, what is the rise time? Calculate the delay to 0.9 of the final value, then subtract the delay to 0.1 of the final value. This gives you the 10% - 90% rise time, which is 2.2*RC. Now multiply the two formulas, and you get BW * Tr = 2.2RC/(2πRC) = 2.2/2π = 0.35. There you go! And yes, RG-59 is a 75Ω cable being used in a 50Ω environment. Both sides of the cable need impedance converters which can be done with resistor networks. The cable mismatch is the cause of the ringing (transmission line reflections, actually) that Dave cites in his video.

[@btilm]

I am in high school and want to major in electrical engineering. I have been researching various things and have always seem to come across your videos. They are very helpful and have helped me a lot. Subscribed. Thanks for everything you've taught me :)

[@T3sl4]

I've built a few of these -- not all transistor types do it, supposedly diffused junction types are required. Surprisingly, I've always had good results with 2N3904s (various makes and dates), an epitaxial type. They're probably a little slower than the '2369s, but faster than my scope in any case. Transistors that don't break down may need different bias current (if it doesn't snap on and generate a pulse, it simmers like a zener), or different B-E resistance.

[@atamasuzu]

add a 2-50m open coax in parallel to C2. It will give you much longer pulse with fast rise time. Jim did it as well in later revisions of that circuit.

[@JoeDesbonnet]

I can observe avalanching in a Philips/NXP BFG424F (ordered 10 and tried just one so far... and it works). Breaks down at about Vce=30V. My pulse width is much wider (50ns), but that's almost certainly because I'm using a breadboard for the moment.

[@Torogol85]

I saw this circuit in AN-72, which discusses the applications of the LT1016 voltage comparator, which was replaced by the AD8561

[@karlmartell9279]

As Jim Williams said: Never touch a running system with your dirty fingers!

[@svenhoek]

RIP Jim Williams

[@Tuttomenui]

Samtec didn't have one either. I did however build a BNC to BNC cable of 800mm length in the parts builder and it had the option to sample the part ( RFA6T-74SP3-74SP3-0800 ) . They are pretty cool for sampling cables I have found. I even sampled a 2 port usb through whole plug from them to replace a broken one on a motherboard.

[@pasihein]

Somebody should write a book about Legendary circuits. This should be on first page. Nice apparatus for anything. Cable length and reflection measurement TDR etc. Thanks Dave for good explanation.

[@aduedc]

To make it even faster, one need to reverse bias the base to emitter junction, so base should be at negative voltage. -- from solid state physics the minority carriers in the base region will swept away when the PN junction is reverse biased. To make it faster yet, reverse the transistor so the emitter is in place of collector. In this case because of doping profile of NPN transistor ( something called collector efficiency) the speed is even higher. To test this reverse the transistor and connect the base to negative voltage, and hope to have a scope that is fast enough to measure it.

[@Steaphany]

Dave, To characterise the pulse, instead of a home valued super scope, why not use a Spectrum Analyser and simply work back the rise and fall from an inverse Fourier transform from the spectra ?

[@metalmolisher666]

He Explained it - the Human body can function as an antenna - he catches teh 50Hz signal that comes from the wireing in yoru room etc and overloads the circut with it. I Once build a -1V/nA Current voltage amplifier - when i moved my hand over it i could measure teh 50hz signal as soon as i got within 20cm of the curcuit. That also explains why you need a good shielding.

[@jvcrules]

that's a brilliant.to generate a fast pulse, I never would have thought of it!

[@tjaeoij32]

Isn't RJ59 a 75 ohm cable? Also, rather than a really fast scope, can't you look at the output of that board on a spectrum analyzer and infer the risetime?

[@JoeDesbonnet]

How difficult would it be to modify this circuit to be a one-shot pulse triggered by a rising/falling edge of a MCU IO line? I'm thinking short range UWB radar ...

[@davidcole6236]

RG-59 ??? How are you matching that 75 ohm cable to the (I assume) 52 ohm source and 'scope impedance?

[@seinfan9]

May be why he's getting that slight ringing. Load reflections due to the mismatch.

[@Nermash]

Why the 10k resistor at the base of Q1? Intuitively it seems that low impedance connection would be better?

[@JoeDesbonnet]

hmm... guessing a FET in series with the BJT (with the gate to the IO line) might do the trick provided it's switched off as quickly as possible. I love this idea of 'abusing' transistors :-)

[@sbreheny]

Hi Dave...you said that you were using RG-59? I think that is 75 ohm coax so it would probably be better with actual 50 ohm coax like RG-58.

[@Nater_Tater]

i was very excited at 03:48 when you pressed down on the bnc and the signal goes crazy what caused that?

[@FennecTECH]

what was that flash at 3:49?

[@JoeDesbonnet]

Is there anything particularly special about the 2N2369? Are there other good candidates? Googling around I see mention of Philips/NXP BFG541 avalanching at 50V (also at Farnell for about EUR 1.9 ea -- same as the 2N2369). Anything else?

[@robertfenney]

How about running the test on the Rogol scope....

[@JosefdeJoanelli]

What are you going to use you're new 1 GHz bandwidth for Dave?

[@0x07AF]

@Peter Mortensen no u

[@EEVblog]

Realised that after the fact. He shouldn't have put his surname first on the silkscreen!

[@正直誠信]

We are using the same Jim Williams pulse generator. The pulse rose similarly to your pulse in the video. But it fell exponentally not symetrically as shown in your video. Can you please comment on that? p.s. we were using a 100MHz TeK oscilloscope to monitor the pulse.

[@Cynthia_Cantrell]

A 100MHz scope isn't nearly fast enough to measure the rise times of pulses as fast as those in this video / circuit. If your circuit is as fast as that shown, what you are mostly seeing are limitations of the scope.

[@正直誠信]

@@Cynthia_Cantrell Thank you. I will try to locate a 500MHz oscilloscope to observe the pulse.

[@Cynthia_Cantrell]

@@正直誠信 Good luck, and have fun!

[@skonkfactory]

I'd really like to see what the cheaper Rigol scopes manage.

[@1ManWrenching]

Please try this on a hacked Rigol.. Kept hoping you'd do that before the video ended.

[@VampireOfIDM]

is peak voltage out from that only 50mV??

[@Radplus]

Hi for traveling a very fast rise time pulse signal from one board to another have i use coax??? If I use normal two wires can it decrease the rise time of pulse???

[@jimmuehlberg2153]

Yes. You need a transmission line. must be 50 ohm, like RG174, and must be terminated and must be short. Like Dave said in the video, the long (cheap) coax causes the "tail" or ringing.

[@Radplus]

@jimmuehlberg2153 thanks👍

[@andrewverran3498]

Newbie here...can you use this device for calibrating an older 25mhz CRT CRO?

[@jimmuehlberg2153]

Well, you certainly don't "need" it. This device will verify the actual bandwidth of your scope. (Once the scope is properly calibrated).

[@andrewverran3498]

@jimmuehlberg2153 I watched W2AEW Alan calibrate a Pintek Oacilloscope, one of the required devices for the procedure was a Pulse generator with a minimum 2ns rise time ? Hence my question. ✌️ ☮️

[@Nater_Tater]

oh i must have missed that i often do a little skipping in his videos to get passed the slower and repetitive stuff no offense Dave i Thoroughly enjoy your videos! =] so basically he is ground and it was screwing with the way the scope was viewing the signal with respect to his body I'm sure it has something to do with the resistance of his skin too right?

[@peterh5165]

Good video!

[@laurent9255]

1 Mega Ohm resistor ??

[@AshleyVanSteenacker]

greetings from Belgium :)

[@EEVblog]

If I did I would have used it. I thought I had one, but it's MIA.

[@gerjaison]

Nice DSO!

[@johnwest7993]

"And Bob's your uncle!"

[@filin587]

that in the scheme?

[@Chooseyouruniquehandlebyaddin]

8:48 630 ps?? u mean 530rite?

[@KiLMaN9542020]

No, i'm french and it's phonetically "manoh" Apart from that, great video ! :)

[@王震-q9v]

I found a book called Triggering of Avalanche Transistor Pulse Circuits, can anyone help me find the PDF version, thank you very much!!!!!!!!!!!!!!!!!!!!

[@internet146]

When is Australia going to upgrade their power to 60 Hz? :3

[@salat]

Will Dave eventually discover that he's using Sylvain's surname all the time which sounds rather strange? Fyi: Sylvain Munaut (I'd pronounce it like "manoh" :) is a team member of the Osmocon Open Source GSM project and can be seen here: watch?v=fH_fXSr-FhU

[@josegilbert8337]

I have a question i need help plz someone help im just getting into the oscilloscope i have acouple car amplifiers that are not workin that i want to out and see if i can fix i have a tekronix 5110 can i use a pulse generator? Or would i nees a function generator? Plz help im new and im tryin to learn

[@demef758]

Audio amplifiers use sinewaves to test them, not pulses.

[@tubegoro]

0oououououói

[@EEVblog]

Yes. Goof.

[@rcwieka9812]

DO EXPERIMENT TO MEASURE BODY CAPITANCE....HOW DO IT?

[@corlfranco9371]

that voice ....

[@EEVblog]

I had one, it's MIA. Plenty of the other sex.

[@randacnam7321]

Ba dum bum tssh.