#203

[@BryanByTheSea]

Thanks, great video. Love re-watching your older videos. Content is still relevant today.

[@rrangana11]

I am one of your later subscriber(early 2015)....watched most the your older videos... ..Knowledge is power, Knowledge is secret of success... Thanks for sharing all your secrets.

[@TheBdd4]

Just saw this revisit, but thank you for another unselfish and excellent lesson.

[@W1RMD]

Thanks for the video and great links to "free" test equipment. I will build this. Thanks and 73's!

[@BMRStudio]

I cannot believe, who can press and why the "hate" button. What's wrong with this video? Thank You for this video W2 :) I pressed the "like" :)

[@clktlk]

Thanks for sharing your knowledge. Great videos!

[@nickpelov]

I can see the benefits of making this oscillator - self containing device and you can even power it from a battery for convenience. I'm asking just out of curiosity - for the experience. If you remove the oscillator and just use the schmitt triggers for sharp edges, then will it have the same effect if you connect your not-that-great signal generator to it. Maybe use the one from the oscillator for double buffering. Of course the input should be properly terminated.

[@ornithopterindia]

👍Thank you sir.

[@ernestb.2377]

Nice little project. Keeping the frequency some lower the circuit can be used to test the capacitors (as you also did in another video), as you have longer periods to charge. I am thinking about the influence of the through hole resistors (inductance). Probably the cause of the ringing? Okay, as ringing was not an issue for the main purpose of the circuit, I am thinking would de rising edge be even faster with smd components? And question about the buffer ports, what is the main goal? As 1 port probably can drive these small loads and is also a low impedance output.

[@w2aew]

Yes, it would be a ittle faster with SMD components. The gates were paralleled to ease the drive needs of each stage.

[@-vermin-]

I remember building a unijunction transistor based TDR circuit many years ago. The pulses had an incredibly fast rise time for a very simple circuit - just a few passives and the UJT. It's a device that doesn't get much attention nowadays. Perhaps worth a video?

[@Mythricia1988]

Verm1n That would be great. I've heard of the unijunction transistor before (Often called a "programmable" unijunction transistor, PUT, I think?) but never really got a grasp on how it worked. Looking at the tiny offering on Digikey I guess they aren't hugely in demand.

[@w2aew]

Verm1n Yeah, if I ever get my hands on some, I'll consider a video on them. I am planning on doing a video on tunnel diodes (another esoteric device) at some point too.

[@jerryhubbard8578]

***** Alan, would love to see these videos. Some from Reflections III would be great.

[@mrjohhhnnnyyy5797]

***** Yeah, that will be interesting 'cause my scope uses tunnel diode for triggering. If it dies, scope basically becomes an scrap pile. REALLY hard to find 'em

[@w2aew]

MrJohhhnnnyyy My video on the tunnel diode is now published: kzbin.info/www/bejne/hqaqaXZ5iseaa5o

[@jimadams2473]

Another great video. Thanks

[@RobB_VK6ES]

I'd be interested to see a SMD version. Probably some performance benefits to be had right there. One thing that has me intrigued is the red frame on the CRT on the old Tek CRO. What is that all about? cheers Rob

[@w2aew]

Rob B That's the graticule backlight on the Tek 2467.

[@joopterwijn]

I looked up you scope, well the multiple domain scope MDO 3104,... I almost got a hart failure :-O That puppy is out my range :-)

[@Mythricia1988]

Joop Terwijn I believe he works for Tektronix, so either he has a great position within there or he gets the occasional freebie x) Leaving the rest of us green with envy either way, right!

[@michaelrcolton]

Joop Terwijn Don't watch his videos where he was testing the MDO4000, it makes the 3000s look cheap!

[@FlyingShotsman]

Hi Alan. I just re-watched this series of videos on your pulse generator and TDR measurements, and I have a question. If my oscilloscope doesn't have a setting for 50-ohm input impedance, should I tee in a 50-ohm terminator at the scope input when I use this TDR circuit/technique? Thanks!

[@w2aew]

For the cases where a 50 ohm termination is needed at the scope, a Tee with a terminator will work in many applications.

[@FlyingShotsman]

Thank you!

[@PapasDino]

Nice update Alan, ok, I gotta build me one now! ;-) 73 - Dino KL0S

[@w2aew]

Dino Papas Thanks Dino. Probably get even faster edges if you use an SMT 74AC14 device.

[@RafaelSouza-xq6vw]

***** nice video! Perhaps even better if using a higher density board with SMD devices... (just ignore that... I completely missed the word "SMT" above...) BTW, I can't help but think why would someone dislike this absolutely straightforward video... Go figure.

[@robertcalkjr.8325]

Thanks Alan.

[@larryrenaud7462]

Alan I have watched all of your videos especially like the TDR videos showing practical ways to measure cable length and termination. But I think that the pc board is in error, it should read "TDR Pulse Generator w2aew " acknowledging the original designer. 73 ve3bhm

[@ethanpoole3443]

In fairness to both, Schmitt triggers have been used as both oscillators and pulse generators by many, including for this very purpose. I'm sure Alan's video introduced many to this circuit and the idea of TDR, but the basic circuit itself can be found in very similar form all over the place throughout the decades. Alan's great contribution are his videos demonstrating its use and for choosing and demonstrating an inexpensive pulse generator that nearly anyone can afford and build (after all, he could have just gone ahead and used a dedicated pulse generator, as I might have, to demonstrate TDR).

[@dwDragon88]

I have some SOIC 74AC14s on hand. I'll do up an SMD version and test it out!

[@w2aew]

dwDragon88 You might need a scope with >1GHz of bandwidth to accurately check out the edge speed, particularly the fall time!

[@dwDragon88]

***** Wait, so my Rigol DS1074Z won't cut it? :) There's a high bandwidth LeCroy at school I can get some time on.

[@RobB_VK6ES]

Alan, I realise it's not really your thing but is their any chance of you borrowing and demonstrating the TEK RSA306. pros and cons of PC based instruments. Cheers Rob

[@w2aew]

Rob B I've got an RSA306, and have done a few vids for "work", but nothing for the channel yet. It's been on my to-do list for a while.

[@RaffysRedstoneLab]

can i use a 40106 cmos schmitttrigger inverter as replacement for the 74AC14 ?

[@w2aew]

+Raffy611 It will oscillate, but the edge speed might be too slow for the inductor "ring" test.

[@siavasharash5448]

One resistor more than your board seen on that board he sent you. What is that resistor and its value?

[@larrybud]

For the LED. While the blog post isn't there anymore, the link to the board is, and you can see (barely) the R7 go to the LED.

[@guytech7310]

Another fast Pulse generator for TDR: www.aholme.co.uk/Avalanche/Avalanche.htm This might make for an interesting video.

[@godfreypoon5148]

Don't let the OH&S people see those edges, they will make you put a guard and interlocks on it.

[@godfreypoon5148]

@Peter Mortensen Those waveform edges are very sharp. Someone could cut themselves!

[@MarkG0MGX]

If anyone wants one of these PCBs in the UK - drop me a line - I have 9 spare right now. Mark G0MGX

[@wolfgangsnitsar4739]

I guess you wouldn't mail one to Florida huh? KV4ATV ... Cat 5/6 Hurricane Michael survivor... 10/10/2018