Who on Earth thumbs videos like this down? w2aew educational videos are so easy to understand thanks to the awesome and concise explanations of essentially complex physics phenomena that I'm sure he could explain quantum theory or thermal dynamics to a 5-year-old, and they would get it.

It is so very enjoyable to listen to someone with such a thorough knowledge of electronics. Thanks.

I am SO GLAD to see you back again ! When youtube announces me that you uploaded somwthing I am sure I will learn something new in a proper way. It's been a while ...

Great presentation Alan. Merry Christmas to You and Yours!

Excellent video, TDR always seemed very mysterious and demanding technically and it’s encouraging to see it done so simply

I wanted to suggest this to some people I was working with in the field at a radar site. They were a mixture of EEs and technicians, and had no idea how to determine the distance down the line, of a fault, without specialty test equipment. I have an ME, but have little EE coursework under my belt (but I have a lot of experience with oscilloscopes). I was not confident enough to suggest anything, and the people at site didn't want to hear anything from me anyway. Glad to see it might have worked.

This method is much easier than unwinding, measuring, and rewinding a reel to get length. Very much appreciated, N1QDT

I vouch from personal experience this technique to repurpose a 100m section of 19mm dia SHF triax feeder for a microwave link. The cable had been installed in a semi-permanent location but at the weather gland where the it entered the transmitter hut there had been some damage that had left the cable under unnecessary bending strain in direct sunlight during day eventually resulting in a dead short of the inner conductor to both outer screens. The run was replaced with new but shortened lengths from the 100meters can be be used on other jobs as cutdown spare lengths. Where to cut was the quandary and with no obvious recorded marking of the damage point nor any deformity i chose to use TDR. The result was that when i put the cable cutter through the calculated distance point it was right on the centre to outers short! That was a great feeling to see Physics & theory come together! There was a small section where the dielectric had softened probably in the heat of high summer over many cycles allowing the centre conductor to eventually move enough & finally touch the two concentric braided conductors.

In case folks are here for methods of estimating remaining cable on a spool, you can always weight it, subtract weight of an empty spool, and divide by weight of some known length of cable.

So pleased to see your return to KZfaq, Al. I learn each time.

Wow.... all those years I scrambled to find a TDR at work.... and thought I could never measure length myself without a TDR! Thank you Alan... I can do it now right at my operating position! 73 KK0DJ

Every time I look at your channel I find a gem. Thank you!

Nice short and quick test method there Alan. If you have the scope available the rest of the parts are likely to also be there, and you just need the T piece and the wire ended resistor, the adaptor is not needed, as you can simply put the resistor end into the T socket, and touch the battery to both.

Your channel has an excellent signal to noise ratio , which in the days of millienals consuming bandwidth on anti social media , with much noise and hardly any signal is a welcome reprieve .

Not sure why this was recommended. Turned out to be much more interesting than I thought it might be. Will certainly look at more of your videos.

School tells the theory. It sure is nice to see it demonstrated! And fun too. Your videos are awesome learning tools!

Alan, you NEVER cease to amaze me. Thanks for the great presentation! 🤠

You're very confident in your presentation, and thank you for taking the time to edit these videos. They each tell a GREAT story! I wish you had been my electronics instructor in high school, it would have been neato! :) good to see you back!

People will be referencing this very useful video for years. It was simple and very educational.

WoW, this is a great learningvid! Really clear, complete and helpfull! Or most great one this one is the supereasy super usefullness! Thanks for your knowledgesharing!

Merry Christmas and thank you for your excellent content over the years. Stay safe.

Missed your videos, haven't done catching up for a while. Excellent as always!!!

Wow. So simple. Can't believe I've not seen it done before. Much more accurate than cutting off an known length and measuring the capacitor ratio of both. Thanks for this tutorial.

That's about as simple as it can be! I was about to build the TDR based on the 74AC14 to test the integrity of some cables and it seems I no longer need it :-) Thanks for another very pleasant and informative video!

Great demo! I love simple. Thanks! Years ago, I used a similar technique to resonate a coil and capacitor for 14.318MHz VCO in my very first video frame grabber. (The literature of the day was obsessed with 4fSC at that time) I wound a few turns of coil on a hunk of chopped off Bic pen, put 22pF cap (representing the varactor diode I planned to use) in parallel with it and AC coupled a pulse from a 555 timer running at a couple hundred Hz. I then looked at the ringing of the LC combo on the scope. The scope was triggered on ch2 directly from the 555 and ch1 showed the ringing of the LC. I tuned it 70nS by adding / subtracting turns and in less than 5 minutes, Bob was my uncle!

Hi Alan, Thank you so much for this series of videos! I’ve built your Schmidt trigger generator and it works like a charm! I used a 74AC14 smd chip and 1% resistors, and I put them in a shielded airplane junction box that I had lying about. I powered it up with 3V and I got a rise time of 4ns. Right now struggling with crappy cables. Thanks for the great videos! Cheers, Mark

Surprised how well this works! Thank you :)

Fantastic video. I am a newbie electronic hobbyist. Good explaination on use of the oscilloscope. I'm going to make this my next project. Thanks for a very easy to understand tutorial.😁

Learned something new today - Thank you for demonstrating / posting!

you are a true inspiration to me when it comes to indepth electronics

This is fantastic. I love simple solutions using gear I already have. Cheers.

Revisited #37 😝 from eight years ago, time flies when you have measured fun!

Awesome practical applications explained clearly, thanks for all the tips.

Time was, scopes were unknowable to many - a scary icon of the arcane. Then there was the Alan Channel. Thumbs up.

Thank you, once again, for a very helpful presentation. This will certainly help with approximating the coax lengths around my place.

As usual, nice and informative video. BRAVO!

Brilliantly simple. Great video. God bless you

Good video, subscribed. I had wondered about trying this on wires to my well pump to figure out how deep it was. Sadly the pump failed and I got to measure it the hard way.

Always love your perfect videos!!! Happy Holidays to you and your family! Merry Christmas and Happy New Year also. But I wish you mainly good health or at least better health & love!

I just found the break in a guitar cable using this TDR technique :D The break was inside one of the jacks. The break was 2 mm before the very end of the center wire inside a coax cable, right next to the tab it was soldered to inside the connector. The delta x was 41 ns so the break should be a little more than 4 meters away, according to the formula. The cable was about 3,5 meters long, so it had to be at the very other end

From Argentina I wish a happy Christmas to you and your family.

So simple, but so clever. Big thumb up !

Thank you for the informative post. Please keep `em coming!

Thanks for sharing. Nice and useful technique.

Fascinating tip. Thank you! 👍👏🏻

Thank you so much for all your videos, you do amazing job teaching us

Very nice presentation, very informative. I learned something new today.

This is another great video i enjoyed watching Alan, absolutely genius how this works - thanks for sharing - enjoy your holidays and stay healthy

Fun to learn and do so with minimal expense while learning a useful trick!

Nice, simple explanation and implementation. I had no idea that amateur radio would lead me to falling down the electronics rabbit hole. And its all your fault! M0YZT

This is so cool! Thank you for sharing!

How to measure a transmission line, the McGuyver Method. :) Great stuff as always! Cheers,

Cool idea. I will try this. Thanks

Really so easy to use. Thank you.

Love this video, Thanks Merry Christmas to you and your nice family from Seyed in Dubai.

Thanks for sharing! This is really cool.

Super simple, super useful, just the right length! Thanks.--73, K2UA

Holy cow, this definitely deserves a like, share, and sub!

Depending on the scope, I’ve used the square wave probe calibration output on the scope itself as a signal source for tdr. Never thought of doing tdr for a roll of speaker wire or lamp cord. I now have an easy way of estimating how long my box of instrumentation cable is too, thanks!

A TDR application I like is on railroad crossings where it is used to calculate the speed of an approaching train so the gates can be down 30 seconds prior to passing the crossing, no matter the speed of the train. This is very handy for big mainlines with 65 mph freight trains and 100 mph passenger trains...

The smart solution is the simplest! Thanks for sharing this! 🙂 👍

Many thanks for this valuable info!

Great video as always

That's great video! And great explanation! Thx

That's a great piece of information Alan, ATB Adam UK

I upgraded with a timer IC and a FET driver IC. Keep this device in my scope kit. I added a 500 ohm trim pot to find the nominal impedance of the cable. I found most cheap "DMX digital cables" are actually built with low impedance microphone cable. They measure 60 to 70 ohms instead of 110 to 120 ohms. This is important if you do stage lighting.

Oh boy - that's just such a useful and dependable technique. Thanks for all your video's Alan, you are a genius as always! 73 de GI8WFA.

Great video sir.

Very informative and simple.

Alan, thanks again for another practical EE video. Never thought you could do a TDR measurement as simple as this. Hmmmm I wonder what happens when you try it on a 3 conductor wire like Romex...

Great to learn something new. Bravo sir, Bravo. Thumbs Up!

This is SOOO useful !

Very nice tip!

Nice. You actually sending a step function signal along the line. No polarity change, only 0 to 9V! As it propagates and reflects - it looks like it only interferes constructively. Doesn't it? Very interesting.

So... could you try this on last years Christmas lights to find where the bad bulb is? Brilliant information, thanks for sharing!

Seeing you move around the cursors, i wonder why vintage analog scope manufacturers never made a mechanical variant of those. I got an old Tek 454a, once a really expensive beast. But while it has loads of features and bandwith that i won't use, i'm still stuck counting divisions by hand. It seems to me that it would have made sense for Tektronix, HP and the other big names of the past to deliver such high end things with slide rule like cursors, or caliper style with a nonius. Hell, perhaps even with a spinning dial like you see on some micrometer calipers. I would've expected it to be a major selling point. Hell, for the highest of high end stuff you could make some mechanical linkages between time/div switch and several scales to mechanically calculate the period time, perhaps even to indicate the frequency... Not as accurate as a real counter but i can imagine that it would definitely come in handy.

Pretty cool experiment could use this at my school.

Fantastic method; this also explains why some LED lamps never turn off using the same principle!

Excellent !! Hugs from Brazil ....

simply mind blowned!

Real good stuff!

Great video

Very clever! Thanks.

Merry Christmas

I agree with all you showed. Have done that myself. But like in radars, you can do with some other way, often called Chirp. Too bad that goes to the opposite dirction from the basic idea of most simple instrument requirement. You would need some sort of sweep frequency source, although I speculate that I could do it by finding the different resonant frequencies using a grid dip meter. Or maybe that is too much of history by now. Maybe a FET dipper?

I liked it. Thanks

I’m liking this! Thanks Alan! 73’ de OZ2BO

Thank you very much for this very clear explanation. What would be different if you didn't use a resistor? Would it not work?

It kept telling me my 50ft cable was only 40 ft long?? Couldn't figure out why, then I measured it...Oops! Great video.

Super 👍

Could you measure the single wire spool using a slightly different, but similar technique? Like if you have access to both ends of the wire on the spool and used two channels on your scope, could you still measure signal propagation through the spool by timing the difference between the rising edge on one channel and the rising edge on the other channel? You'd have to remember to not divide your result by 2.

Nice. For single conductor, would access to both ends plus a 2 ch scope be measurable. I will have to experiment next time i am in the workshop.

I was thinking of the 120 Ohms termination rezistor of the CAN Bus. If you add a rezistor at the end or short the end it won't work right?

Спасибо ☺️

Very good

Excellent video, Alan! This video also explains why you can have a high SWR on your antennas, due to the reflected energy. I don’t know if you know much about physics, but now that I’ve seen your video, you have me thinking. Why does the energy reflect back into the wire, and not simply dissipate from the end? I’m guess that it has something to do with the wire being a better conductor than air. Any thoughts?

Great Job, Have you tried this type of measurement using waveguide such as WR62 (KuBand) ???

I am looking at buying some sort of analyzer for making antennas and doing reactance/impedance measurements etc. For feedline and antennas. For what I am doing is it more feesable to buy a nano vna, mfj 259c, or one of those sark100s? Thanks and Merry Xmas!!

A good follow up is on short circuit v open circuit or damaged cables

Very Good :)