First I built this circuit on breadboard. The impulse at the output of the TDR head was - of course - very small, 1-2 V (depending on the transistor) and both the rise and the fall time were above 2 ns. After having made the final (non SMD) version of the TDR head (built on a BNC), the parameters got very close to those seen in the video. After changing the capacitors of the voltage multiplier to 3,3 nF and bridging the 100 Ohm resistor by 7 pF capacitor, the output impulse increased to 12 V, the rise and the fall time dropped down both to 920 ps, i.e. the shape of the impulse is pretty symmetrical. Thank you very much for this nice project. Greetings from Hungary, Peter
Wow... bravo!! Thank you Mr.Carlson! what a wonderful design and build. This is the first time I have seen the usually troublesome, bipolar transistor avalanche breakdown mode put to good use.
This is something I can really appreciate! Well explained and no embellishments. The math so far is really too simple at this point. Waiting for more! Who needs to spend a few thousand on an Anritsu TDR. 73!
True story of an electricity supply company underground cable division , a long time ago. They had an experimental machine in the back of a small truck and it told them at what distance away their buried power line has a fault ... and where exactly to dig down into the ground. They didn't use the machine very often but when they did use it always told them the distance to dig, so they dig there, they wouldn't find the break there, then they have to dig along either direction to expose more cable to find the break. After quite a few years they realised the break is always each time exactly 6 feet away from where the machine says it is. Then they realised that for all of the years they had been using it they had not been including the length of the hook up cables in between the machine and buried power line. And yes they were following the instructions to the letter.
I remember a lecturer at trade school who clearly loved explaining the concepts he had mastered. We used to follow him around during coffee breaks in the hope of more brainfood. People who werent interested in his topic thought he was a chatterbox. But we thought he was an absolute goldmine. So many people missed him when he retired. Hint-hint.
Marvellous, focussed and highly articulated, easily understood without being a "my first circuit" type channel. Proper down to earth but hardcore electronics without any nonsense. You make "EEVblog" look like a kindergarten for simpletons.
True, but a little harsh. "Kindergarten" or "for simpletons", but not both. EEV is a different target audience. The difference being this channel, while highly articulated, is completely useless to someone who is not neck-deep in the hobby or a degreed Engineer. The proof: my wife will look at the screen for a up to 20 seconds of EEVblog before telling me to change it. This one gets the insta-scoff. This channel also compels a lot more "device-envy".
I am retired and don't move very fast anymore :-). I have been a computer and banking equipment all my working years and enjoy the tech side of ham radio. I am still learning from your channel and enjoy that you talk about older equipment and test gear as that mostly what I have. From the time I was in the USAF at 18 until the 80's I carried a Techtronix 535 Scope and I still have one today. It has sent for calibration a few times, but has never broke nor lost a tube! I really enjoy your videos. Keeo it up! Thank you. R. Scott (Scotty)
THANK YOU for TDR video. I first used TDR in early 1980s. Understanding the propagation-speed thru specific cable-type helps pinpoint things. I actually made a "nanosecond ruler" for my toolbox at work. I helped build testers for computer-chips (memory/CPUs) and had to trim length off of cables to calibrate the timing-pulses presented to the chips on the wafers.
Giving a shout out to your better half. Her photography is simply stunning. I'd like to encourage her to do this more often though I suspect she has a hand in most of your video's. Cheers.
Paul, you are an excellent teacher. I know it takes a lot of time to make these videos, but they are really enjoyed and appreciated. I have spent my life working with electricity and electronics, and am still learning.
This is the best name for a piece of test equipment so far. If i build one of these i will feel like Dr Who but should also never be without the MRC Tracer probe
The TDR I used way back when had an old print roll feed to give a full trace hardcopy, really old but few knew how to use it. I took the time to figure it out, saved me loads of time checking aerial cables, even came in useful on gore/times cables. Always made me laugh telling my boss it was a thru hole connector that's got a bad screen and he'd look at my like I was nuts.....yet proved right when it gets changed and the problem is fixed. Took a while but eventually he gave up and just asked me 'teach me' Wrote up a whole guide for him and the other techs, even built up a kit of connectors and adaptors to make it easier. Good times. And a very interesting design
Hi mr Paul, you're a great man. Your videos are very different than the others, because it's real and transparency.. every words that you spoke are legit with visualization and you provide us a schematic in details and it's so nice. Excellent I feel my self sitting on the classroom listening to you as my teacher. Fot that it's a big thumbs up for me..so thank you for sharing your knowledge.
That’s amazing. 350 volts from one C at 1.5. V. Lol. I remember as a kid someone I knew had a very nicely made miniature electric chair. It was made of wood with copper plates all over it. Very realistic looking It was hooked up to a 9v battery and when you touched any of the plates , basically any part of the chair. You got one hell of a shock. I was fascinated as a kid by the thing.
In the early '70s I worked at HP and used a TDR (model 1818, I believe) to find and fix discontinuities in the microwave test equipment we built there. It used a step recovery diode to generate pulses and could resolve DTF to within 6mm or better.
The first macro picture your wife took of the BNC connector is truly a work of art. If she doesn't mind, I'm going to use it as a wallpaper on my iPad. Please thank her for me and pass on my compliments.
Yes, I have a problem collecting oscilloscopes! But I can quit any time! 😄 Great job on that TDR, as well as explaining it! I love your tutorials. So thorough, yet relatable.
Built it, works great. All thru hole parts, but 100% stuff on hand, gotta love that. Minor tweak due to xsistors in power supply. subbed 82 ohm for 560 ohm and runs on 3 volts (2 x AAA). Second head built works better. Used 1/8 watt resistors so there basically are no lead lengths. Just found your channel last week. Keep up the good work. 73, John
I first ran in to TDR equipment 17 or so years ago, when i was a very young engineer at a cable operator in Ohio. We were a *small* cable operator with around 1,800 subscribers, but were trying to grow. We had approximately 4 miles of underground distribution likes, and another 2 or so miles overhead, so fault tracing was difficult at best. My predecessor bought a multifunction CATV analyzer, and he had the forethought to also order the optional external TDR unit. I've used TDR to find faults in coax on and pff aince then, both in my CATV career and my amateur radio hobby, but I didn't fully understand just *how* it actually worked until today! The TDR analyzer I use connects to an excessively complex coax and CATV analyzer, and the pair always give a distance measurement in feet or meters, but you do still have to confirm what coax you are connected to.
Thanks for your video. You made a nice circuit and took the time to clean-up the wave shaping. I was a bit lazier and just used a step-recovery-diode and pulsed it since I just needed to do a couple of measurements. Nice to see that you didn't use a bunch of exotic parts but things that we could have around as hams. Thanks Again!
Decades ago we visited a Tektronix engineer developing a TDR instrument in a biz park in OR. He had spool of fiber optics cable that he said cost many thousands of dollars...but he said it was the future.
Excellent video - always wanted a better understanding of this. Stunning macro photography from your partner - how lucky you are to have her support and enthusiasm too.
This is a great tutorial! I believe this is a derivative of the Jim Williams pulse generator from one of his Analog Devices articles, but with a simpler HV source, and an adaptation to make it work with surface mount parts as well.
On one hand, I'm impressed that YT managed to recommend something that's actually relevant to my interests. On the other hand. I did all the things in the introduction already, probably 15 years ago? I could even tell if a cable was faulted short or open by the polarity of the reflected signal. Welp. It certainly is what it is. I think I was mostly using an AN/GRM-122. So slightly higher end than what you made here. Obviously I didn't make that though.
Wow, I have never thought that a standard transistor like the 3904 avalanches that reliably between base and collector and quickly shoots the energy stored in the capactitor right to the emitter.
Not wanting to b cloned .... still and peaceful and excellent . . . After Virtue. Amping up the gain with the-your knowledge as the vari tranzisters used. Watching your posts one-by-one to understand the just-received Knight mini-lab!!
That reminds me of a circuit. I saw a pcb with a pair of traces going perpedicular nowhere. They were shorted at the end. Turns out it's to create a reflection that turns a short pulse into a much shorter pulse. I can't for the life of me remember the application.
Fantastic video. Hopefully I will be able to have one made and use the two oscilloscopes for the first time,scary thought as i'm an mechanical engineer.
Nice video. I made a TDR myself with a schematic i found on the internet, using a 74ac14. IT Works welk, but the signaal of tour ter looks a lot cleaner. If you should ever decide to sell your tdr in kit form or juist the pcb let me know !
great explanation. hoping in the future to learn more on how frequecy affects the function of this setup and which range works the best. thanx for he video btw those sweep shadows on that scope are so annoying!!!
I particularly enjoy the "C'English to 'E'English" uses that I saw in some places on your paperwork. some parts are in Brit, and some are in American. It just seems to me that it demonstrates how it's more convenient to use one convention in one context, and the other in another place. (I'm assuming that you're from the beautiful 'Great White North' above me- I'm an Oregonian.) Oh well. I guess it goes with the territory.
Makes me want to retire my old HP tdr. Thanks for the excellent vids. In school they never told us how smart Canucks are!! I wish I lived closer to you we could take over the Universe! Say, do you think the tdr head will work with a nano scope?
You should have come down to Yuma with me. I got a large box truck load of old O Scopes with Polaroid cameras for $2000. Some of the scopes worked and some were cannibalized to make other scopes work. The cameras were scrapped.
Can the pulse generator be reliably included on the same PCB as the HV generator? Just thinking if opening a modern USB power bank and removing one of the 18650 cells and using the space to house a PCB with the circuitry could make a pretty compact unit and should fit into a circuit with the form factor of the removed cell. Lots of power and easy to recharge and can be used for other tasks like a torch (often included) or powering a PineCil soldering iron if the powerbank has 19V support.
One thing i don’t understand is why we want to duplicate the stray inductance caused be the leads in the through hole version. That doesn’t seem like a feature we would wish to mimic. Thank you.
I thought that in the scientific world, we rather use the metric system. But for the rest of the planet, our conversions will be made ... Very good video anyway.
+Mr Carlson's Lab I also wondered, cause all the formulas are in SI units. Wouldn't it been better to convert the inches to meters instead of converting the formulas?
you can make microphotos like that using a document scanner and retouching gamma, equalizer and so on with photoshop, even discover hiden details ,and about your videos very good job , my thumb is UP!!
Great Video and smart circuits. One question still: why the head needs so high voltages? On the scope screen the initial pulse is about 8 volts only. Wouldn't it work with lower voltages from the supply circuit?
Axel Haar Hi Axel, It takes High Voltage at low current to make the transistor avalanche. If you look up "transistor avalanche" on the net, you will get some descriptions of how it works.
Mr Carlson's Lab Ah, I didn't know the Transistor Avalanche effect up to now. Now I understand how you manage to get so fast switching times! Thx a lot.
Frank T To get such short rise times you’d need 100EP or faster ECL logic family, and that’s a bit more demanding to implement than an avalanche pulser circuit. You’d need something like a ring oscillator with perhaps a bit of gain to keep the circulating edge rise/fall times as short as possible. It’s way more transistors inside many chips, requires very careful thin two-layer laminate ground/power plane prototyping (typical 2-layer PCB is too thick - you need the distributed capacitance), and is generally more expensive and more painful to get working in entry-level amateur conditions. The old 10k ECL family is very docile and can be prototyped with wire-wrap, but here you need an order of magnitude faster transition times than the old 10k ECL logic. The modern “1 00k” and “1000k” derivative families are suitable, but those are tiny packages and really require a 4-layer PCB to work reliably. Those are absolutely minuscule packages often as well. And those chips cost 10-25$ apiece, and you’ll need several of them. ECL is special purpose logic these days. 40-20 years ago it was ubiquitous. Nowadays if you need ECL, then money is no object, because you’re either designing high-end test gear, or high-end RF/comm systems and such. It’s not magic and with a bit of care you can use it, but in terms of obsolescence-proofing your design, ECL chips are not the way to go. Discrete ECL circuits using very fast RF transistors are a whole different story though. Those can be made future-proof and designed to be put together by humans, not robots. Still, lots of attention to parasitic inductance is necessary - sometimes 10mm of a thin trace is too long in those circuits, and a “2.5 dimensional” assembly is required. Rings a bell? :)
What are those beams of light that are shooting off of the reflective surfaces of the still pictures called? Thanks J. And you can almost see the tin whiskers forming on the surface of the connector body.
Thanks for the video.I really want to ask question still on my mind from high school that maybe an upcoming video:How can we measure the frequency of water ?
Is there a way to make a transmission line transmit a pulse at the slowest possible speed. Like 10 percent velocity factor, or slower? Need a long slow delay line.
hmm just wondering if wouldnt be possible with a schmitt trigger to make an oscillator inject the signal into it and measure with the scope the rising edge and reflection of it
Is there anything special about the diodes you selected for this or would a 1n4148 also do? They seem to have slightly higher reverse recovery times but otherwise things like breakdown voltage are better than for those listed.
Quick update on this. I've since then built this circuit with 1n4148 diodes and it seems to work quite well. Haven't been able to test with the original recommended components so I have no clue about the difference in performance but this seems to work for me.
Is the 7.5pf cap. In the head a critical value? I have looked every where for that value with no luck. If it is not what would be a good substitute value?
I got a question, how can you do a TDR not to an open end but to a bend or a shake of the cable. I want to detect where is a momentary vibration along the cable and get the location of it.
Many motion detecting cables have piezoelectric dielectric so they create a voltage pulse when they are struck. The time difference between the pulses arriving at the two ends and the order of the pulses tells you how far from the centre of the cable and which side of the centre the cable was struck. If you pinch the cable enough the TDR will show a small discontinuity reflection but that will be hard to detect automatically.
hey man.. did u know how to build something to test cable SNR or something that can measure 'is the cable good or not for network. sorry cz i bad in english. tq
First I built this circuit on breadboard. The impulse at the output of the TDR head was - of course - very small, 1-2 V (depending on the transistor) and both the rise and the fall time were above 2 ns. After having made the final (non SMD) version of the TDR head (built on a BNC), the parameters got very close to those seen in the video. After changing the capacitors of the voltage multiplier to 3,3 nF and bridging the 100 Ohm resistor by 7 pF capacitor, the output impulse increased to 12 V, the rise and the fall time dropped down both to 920 ps, i.e. the shape of the impulse is pretty symmetrical.
Thank you very much for this nice project. Greetings from Hungary, Peter
Wow... bravo!! Thank you Mr.Carlson! what a wonderful design and build. This is the first time I have seen the usually troublesome, bipolar transistor avalanche breakdown mode put to good use.
This is something I can really appreciate! Well explained and no embellishments. The math so far is really too simple at this point. Waiting for more! Who needs to spend a few thousand on an Anritsu TDR.
73!
Wow you made this nine years ago, forever fantastic lessons one of my favourite youtube sites. Thanks
True story of an electricity supply company underground cable division , a long time ago. They had an experimental machine in the back of a small truck and it told them at what distance away their buried power line has a fault ... and where exactly to dig down into the ground. They didn't use the machine very often but when they did use it always told them the distance to dig, so they dig there, they wouldn't find the break there, then they have to dig along either direction to expose more cable to find the break. After quite a few years they realised the break is always each time exactly 6 feet away from where the machine says it is. Then they realised that for all of the years they had been using it they had not been including the length of the hook up cables in between the machine and buried power line. And yes they were following the instructions to the letter.
I remember a lecturer at trade school who clearly loved explaining the concepts he had mastered. We used to follow him around during coffee breaks in the hope of more brainfood. People who werent interested in his topic thought he was a chatterbox. But we thought he was an absolute goldmine. So many people missed him when he retired. Hint-hint.
Thanks Colin, not retired yet though :^) I will be around for awhile.
Marvellous, focussed and highly articulated, easily understood without being a "my first circuit" type channel. Proper down to earth but hardcore electronics without any nonsense. You make "EEVblog" look like a kindergarten for simpletons.
True, but a little harsh. "Kindergarten" or "for simpletons", but not both. EEV is a different target audience. The difference being this channel, while highly articulated, is completely useless to someone who is not neck-deep in the hobby or a degreed Engineer. The proof: my wife will look at the screen for a up to 20 seconds of EEVblog before telling me to change it. This one gets the insta-scoff.
This channel also compels a lot more "device-envy".
@@moweber If someone is an Engineer why does he need to look at EEV.?
I am retired and don't move very fast anymore :-). I have been a computer and banking equipment all my working years and enjoy the tech side of ham radio. I am still learning from your channel and enjoy that you talk about older equipment and test gear as that mostly what I have. From the time I was in the USAF at 18 until the 80's I carried a Techtronix 535 Scope and I still have one today. It has sent for calibration a few times, but has never broke nor lost a tube! I really enjoy your videos. Keeo it up!
Thank you.
R. Scott (Scotty)
Thanks for taking the time to write Scotty!
THANK YOU for TDR video. I first used TDR in early 1980s. Understanding the propagation-speed thru specific cable-type helps pinpoint things. I actually made a "nanosecond ruler" for my toolbox at work. I helped build testers for computer-chips (memory/CPUs) and had to trim length off of cables to calibrate the timing-pulses presented to the chips on the wafers.
You're welcome Bruce!
Your explanations are very clear.
You are providing very high quality content.
Please make much much more videos.
Thanks for the nice comment!
Giving a shout out to your better half. Her photography is simply stunning. I'd like to encourage her to do this more often though I suspect she has a hand in most of your video's. Cheers.
Thanks William, she really appreciates your comment!
Paul, you are an excellent teacher. I know it takes a lot of time to make these videos, but they are really enjoyed and appreciated. I have spent my life working with electricity and electronics, and am still learning.
Thanks Bill! Glad you enjoying. These TDR video's are pretty specialized, so when people comment here, I know their really interested in electronics.
Fascinating! Going into this video I had no idea what a TDR was but now I do! Thank you Mr.Carlson!
Glad it was helpful!
This is the best name for a piece of test equipment so far. If i build one of these i will feel like Dr Who but should also never be without the MRC Tracer probe
The TDR I used way back when had an old print roll feed to give a full trace hardcopy, really old but few knew how to use it. I took the time to figure it out, saved me loads of time checking aerial cables, even came in useful on gore/times cables. Always made me laugh telling my boss it was a thru hole connector that's got a bad screen and he'd look at my like I was nuts.....yet proved right when it gets changed and the problem is fixed.
Took a while but eventually he gave up and just asked me 'teach me'
Wrote up a whole guide for him and the other techs, even built up a kit of connectors and adaptors to make it easier. Good times. And a very interesting design
Hi mr Paul, you're a great man. Your videos are very different than the others, because it's real and transparency.. every words that you spoke are legit with visualization and you provide us a schematic in details and it's so nice. Excellent I feel my self sitting on the classroom listening to you as my teacher.
Fot that it's a big thumbs up for me..so thank you for sharing your knowledge.
That’s amazing. 350 volts from one C at 1.5. V. Lol. I remember as a kid someone I knew had a very nicely made miniature electric chair. It was made of wood with copper plates all over it. Very realistic looking It was hooked up to a 9v battery and when you touched any of the plates , basically any part of the chair. You got one hell of a shock.
I was fascinated as a kid by the thing.
In the early '70s I worked at HP and used a TDR (model 1818, I believe) to find and fix discontinuities in the microwave test equipment we built there. It used a step recovery diode to generate pulses and could resolve DTF to within 6mm or better.
A TDR can be worth its weight in gold when locating a cable fault. Sure beats the hell out of jumping fences.
Great tutorial. Thanks!
I've come back years later to say, excellent, as usual.
The first macro picture your wife took of the BNC connector is truly a work of art. If she doesn't mind, I'm going to use it as a wallpaper on my iPad. Please thank her for me and pass on my compliments.
No Problem William, glad you like the picture!
I believe you must be the smartest person I have ever seen on the internet.
Your too kind John! Thanks for your comment.
I must agree, makes great video and seems to be a nice fellow.
Very refreshing.
Yes, I have a problem collecting oscilloscopes! But I can quit any time! 😄 Great job on that TDR, as well as explaining it! I love your tutorials. So thorough, yet relatable.
Built it, works great. All thru hole parts, but 100% stuff on hand, gotta love that.
Minor tweak due to xsistors in power supply. subbed 82 ohm for 560 ohm and runs on 3 volts (2 x AAA). Second head built works better. Used 1/8 watt resistors so there basically are no lead lengths.
Just found your channel last week. Keep up the good work. 73, John
scooby45u Good to hear! Thanks for the comment too!
I first ran in to TDR equipment 17 or so years ago, when i was a very young engineer at a cable operator in Ohio. We were a *small* cable operator with around 1,800 subscribers, but were trying to grow. We had approximately 4 miles of underground distribution likes, and another 2 or so miles overhead, so fault tracing was difficult at best.
My predecessor bought a multifunction CATV analyzer, and he had the forethought to also order the optional external TDR unit.
I've used TDR to find faults in coax on and pff aince then, both in my CATV career and my amateur radio hobby, but I didn't fully understand just *how* it actually worked until today!
The TDR analyzer I use connects to an excessively complex coax and CATV analyzer, and the pair always give a distance measurement in feet or meters, but you do still have to confirm what coax you are connected to.
Also, watching the explanation at 15:00 or so, this reminds me of some training I've had dealing with sonar.
Thanks for your video. You made a nice circuit and took the time to clean-up the wave shaping. I was a bit lazier and just used a step-recovery-diode and pulsed it since I just needed to do a couple of measurements. Nice to see that you didn't use a bunch of exotic parts but things that we could have around as hams. Thanks Again!
Man, you're bringing back memories with this one. Learned to use one at USAF tech school for locating wire shorts in aircraft wings/ fuselage.
Don't know why I was expecting the reflected signal to be horizontally flipped xD
Great video, btw
Decades ago we visited a Tektronix engineer developing a TDR instrument in a biz park in OR. He had spool of fiber optics cable that he said cost many thousands of dollars...but he said it was the future.
Turns out he was spot-on! 👍
Excellent video - always wanted a better understanding of this. Stunning macro photography from your partner - how lucky you are to have her support and enthusiasm too.
This is a great tutorial! I believe this is a derivative of the Jim Williams pulse generator from one of his Analog Devices articles, but with a simpler HV source, and an adaptation to make it work with surface mount parts as well.
"Time Domain Reflectometer" has got to be the most "Dr. Who"-sounding thing I've heard all day.
I was thinking Star Trek but Dr. Who is even better. I’m surprised no one else mentioned the science fiction sounding name in the comments.
made up a similar unit & tested all sorts of cables with interesting results --keep up the good work
On one hand, I'm impressed that YT managed to recommend something that's actually relevant to my interests.
On the other hand. I did all the things in the introduction already, probably 15 years ago? I could even tell if a cable was faulted short or open by the polarity of the reflected signal. Welp. It certainly is what it is. I think I was mostly using an AN/GRM-122. So slightly higher end than what you made here. Obviously I didn't make that though.
Been watching your videos awhile, but this one i can use! That's great. Cool stuff, thorough and intelligent. 👍
Wow, I have never thought that a standard transistor like the 3904 avalanches that reliably between base and collector and quickly shoots the energy stored in the capactitor right to the emitter.
“If you have a problem collecting old oscilloscopes like I do “. Lmao.
Excellent video Mr. Carlson!
Great information Mr Carlson thanks for sharing.
+wade hicks
Your welcome Wade!
Great video with excellent information! Things we sometimes forget we knew when we have the luxury of an Anritsu Site Master always handy.
Not wanting to b cloned .... still and peaceful and excellent . . . After Virtue. Amping up the gain with the-your knowledge as the vari tranzisters used. Watching your posts one-by-one to understand the just-received Knight mini-lab!!
Nice. People at work use TDRs. They also use optical equivalents. It'd be cool to build and test one at home.
That reminds me of a circuit. I saw a pcb with a pair of traces going perpedicular nowhere. They were shorted at the end. Turns out it's to create a reflection that turns a short pulse into a much shorter pulse. I can't for the life of me remember the application.
Great videos ! I learnt so much from them .Thank you so much for your time and effort.
Great Work Mr Carlson
Beautiful Macro pics!
Creative video, keep it up, thank you :)
Fantastic video. Hopefully I will be able to have one made and use the two oscilloscopes for the first time,scary thought as i'm an mechanical engineer.
Love the still photos.
Thanks Mancel!
LOOKS VERY WELL MADE 😊😊😊
Nice video.
I made a TDR myself with a schematic i found on the internet, using a 74ac14.
IT Works welk, but the signaal of tour ter looks a lot cleaner.
If you should ever decide to sell your tdr in kit form or juist the pcb let me know !
great explanation. hoping in the future to learn more on how frequecy affects the function of this setup and which range works the best. thanx for he video btw those sweep shadows on that scope are so annoying!!!
Sometime you should do a video on measuring impedance match and bandwidth of antennas connected to coax.
Thanks for your input!
I particularly enjoy the "C'English to 'E'English" uses that I saw in some places on your paperwork. some parts are in Brit, and some are in American. It just seems to me that it demonstrates how it's more convenient to use one convention in one context, and the other in another place. (I'm assuming that you're from the beautiful 'Great White North' above me- I'm an Oregonian.) Oh well. I guess it goes with the territory.
Great video sir......keep it up.......
great build
thank you
Thanks Dennis.
The power supply can be made from a camera flash.
Thanks for these awesome videos!
+ltousig
Your welcome!
Excellent video :)
Hi'gak Iya Thank you!
Makes me want to retire my old HP tdr. Thanks for the excellent vids. In school they never told us how smart Canucks are!! I wish I lived closer to you we could take over the Universe! Say, do you think the tdr head will work with a nano scope?
Thanks for the great video!
You should have come down to Yuma with me. I got a large box truck load of old O Scopes with Polaroid cameras for $2000. Some of the scopes worked and some were cannibalized to make other scopes work. The cameras were scrapped.
+Seth B
I have to be careful, You haven't seen the other room.
@@MrCarlsonsLab I blew out all those 465s & 465Bs on eBay. How many 465s do I need? ONE! Okay, TWO.
Can the pulse generator be reliably included on the same PCB as the HV generator?
Just thinking if opening a modern USB power bank and removing one of the 18650 cells and using the space to house a PCB with the circuitry could make a pretty compact unit and should fit into a circuit with the form factor of the removed cell.
Lots of power and easy to recharge and can be used for other tasks like a torch (often included) or powering a PineCil soldering iron if the powerbank has 19V support.
One thing i don’t understand is why we want to duplicate the stray inductance caused be the leads in the through hole version. That doesn’t seem like a feature we would wish to mimic. Thank you.
Very good as usual.
+Tech Chuck Legg
Thanks Chuck! I have a Tek type 661 scope that will make a great video as well..... in the future. Hope your Christmas went well!
I thought that in the scientific world, we rather use the metric system. But for the rest of the planet, our conversions will be made ...
Very good video anyway.
+Axel LAMBERT
LOL, Glad you enjoyed Axel!
Thanks for the video. I can't wait to build myself a TDR.
I'm curious as to why you are using feet instead of meters?
Robert Calk Jr. My measuring tape has Feet on it. LOL... I bought an American tape :^) Thanks for your comment Robert!
+Mr Carlson's Lab I also wondered, cause all the formulas are in SI units. Wouldn't it been better to convert the inches to meters instead of converting the formulas?
Did I miss it? A description of how the head end creates the pulse? Thanks.
rowifi This explains it : en.wikipedia.org/wiki/Avalanche_transistor Thanks for stopping by!
Very interesting circuit design. I bet you didn't use Spice to design it!
you can make microphotos like that using a document scanner and retouching gamma, equalizer and so on with photoshop, even discover hiden details ,and about your videos very good job , my thumb is UP!!
Thanks Francisco!
I think I'll go with a Schmitt trigger oscillator and keep the voltages low, thanks!
+Michael Hall No Problem, there are lots of ways to do this. Glad you enjoyed the video!
+Michael Hall - That is much simpler but the rise time will be four times longer.
Great Video and smart circuits. One question still: why the head needs so high voltages? On the scope screen the initial pulse is about 8 volts only. Wouldn't it work with lower voltages from the supply circuit?
Axel Haar Hi Axel, It takes High Voltage at low current to make the transistor avalanche. If you look up "transistor avalanche" on the net, you will get some descriptions of how it works.
Mr Carlson's Lab Ah, I didn't know the Transistor Avalanche effect up to now. Now I understand how you manage to get so fast switching times! Thx a lot.
Glad you enjoyed!
When using a 12V AC supply it takes 9 steps (18 capacitors) to get the voltage it takes.
+0MoTheG Better take big capacitors like 2.2uF and fewer steps, because at 50 or 60 Hz 220nF is way to little to stay charged.
That power supply would be a good circuit, with a potentiometer to adjust the voltage, for charging pocket dosimeters.
That is a very good idea. A fixed potentiometer load should provide a stable voltage.
Great explanation on TDR... won't it be easier to build the pulse generator using a Logic chip?
Frank T To get such short rise times you’d need 100EP or faster ECL logic family, and that’s a bit more demanding to implement than an avalanche pulser circuit. You’d need something like a ring oscillator with perhaps a bit of gain to keep the circulating edge rise/fall times as short as possible. It’s way more transistors inside many chips, requires very careful thin two-layer laminate ground/power plane prototyping (typical 2-layer PCB is too thick - you need the distributed capacitance), and is generally more expensive and more painful to get working in entry-level amateur conditions. The old 10k ECL family is very docile and can be prototyped with wire-wrap, but here you need an order of magnitude faster transition times than the old 10k ECL logic. The modern “1 00k” and “1000k” derivative families are suitable, but those are tiny packages and really require a 4-layer PCB to work reliably. Those are absolutely minuscule packages often as well. And those chips cost 10-25$ apiece, and you’ll need several of them. ECL is special purpose logic these days. 40-20 years ago it was ubiquitous. Nowadays if you need ECL, then money is no object, because you’re either designing high-end test gear, or high-end RF/comm systems and such. It’s not magic and with a bit of care you can use it, but in terms of obsolescence-proofing your design, ECL chips are not the way to go. Discrete ECL circuits using very fast RF transistors are a whole different story though. Those can be made future-proof and designed to be put together by humans, not robots. Still, lots of attention to parasitic inductance is necessary - sometimes 10mm of a thin trace is too long in those circuits, and a “2.5 dimensional” assembly is required. Rings a bell? :)
What are those beams of light that are shooting off of the reflective surfaces of the still pictures called? Thanks J.
And you can almost see the tin whiskers forming on the surface of the connector body.
Well done! Thank you.
what is the most basic type of scope to use this with?
epic channel...
Thanks for the video.I really want to ask question still on my mind from high school that maybe an upcoming video:How can we measure the frequency of water ?
abdo mohamed Thanks for your comment!
will be looking forward to your reply.....
It would have been nice if it included the more civilized decimal metric system as well. ;-))
we use OTDR's in the fiber optic industry
Here by accident. Saw the title & thought he might have built a real time machine lol.😂😮😅
Can a TDR be used to measure the break in a wire other than a coax? In stranded wire for instance?
I would have liked to see you run more real world test with your setup.
Would this TDR work with twisted pair instead of coax?
This one is designed around a coax type cable.
Put a 300 ohm pot in series.
Is there a way to make a transmission line transmit a pulse at the slowest possible
speed. Like 10 percent velocity factor, or slower?
Need a long slow delay line.
LOL - I seriously thought this was a SciFi book channel based on the title!
Paul could you modify to a metal detector 7KJ cap bank and a planar coil
hmm just wondering if wouldnt be possible with a schmitt trigger to make an oscillator inject the signal into it and measure with the scope the rising edge and reflection of it
+Alex Verias
I Think Alan W2AEW has made a version of that using a 74 series logic IC.
Is there anything special about the diodes you selected for this or would a 1n4148 also do? They seem to have slightly higher reverse recovery times but otherwise things like breakdown voltage are better than for those listed.
Quick update on this. I've since then built this circuit with 1n4148 diodes and it seems to work quite well. Haven't been able to test with the original recommended components so I have no clue about the difference in performance but this seems to work for me.
I worked as a calibrrtion tech for Tek for 2 years.
This sampling scope had a rise time of 25 pS, light travels at 33 pS / cm
Mad expensive kit.
Is there a parts list available? Some of the parts in the power supply are difficult for me to read.
Is the 7.5pf cap. In the head a critical value? I have looked every where for that value with no luck. If it is not what would be a good substitute value?
Hi MrRickrzr. 10pF should be ok, you will see an increase in amplitude with that value.
Sir, can this TDR, that you made in this video, used in "arc reflection technique" of finding underground cable fault??????
I got a question, how can you do a TDR not to an open end but to a bend or a shake of the cable. I want to detect where is a momentary vibration along the cable and get the location of it.
Many motion detecting cables have piezoelectric dielectric so they create a voltage pulse when they are struck. The time difference between the pulses arriving at the two ends and the order of the pulses tells you how far from the centre of the cable and which side of the centre the cable was struck.
If you pinch the cable enough the TDR will show a small discontinuity reflection but that will be hard to detect automatically.
What kind of oscillator is that? How do you figure out the values? Trial and error?
ChantaFlaite Just Google: transistor avalanche oscillator. That should answer your questions.
hey man.. did u know how to build something to test cable SNR or something that can measure 'is the cable good or not for network. sorry cz i bad in english. tq
Well I'm short with time to build that system from your instructions. If you sell it online I order one TDR from you
What model is that mainframe digitizing scope?
Is this Cockcroft voltage multiplication stack?