Time Domain Reflectometer

[Aztlanpz]

I have created a Time Domain Reflectometer; Let me know if anyone is interested I will post the project.



Azltan

[BradC]

I'd be interested in some more details.

[lwatts666]

Looks very similar to the one published in Silicon Chip magazine December 2014...

[Aztlanpz]

Yes it’s base on that one

[tggzzz]

Specification?

Form that schematic it looks like a signal generator, not a TDR.

[magic]

What's the point of the opamp? It seems to be a unity gain buffer, which could be replaced with a bunch of paralleled 74 gates.

[jmelson]

So, what is the rise time of the output?  If not fast (like sub ns) then it is only useful for characterizing long cables.  I often what to test fairly short cables, around 1 m length.
For that, you need a really fast rise time.

Jon

[magic]

OPA356 slew rate is rated 0.36V/ns so you can imagine...

The circuit below works nicely, I have built it using the dual version of that chip to avoid exceeding absolute ratings on output short circuit. Optimum output resistor for TI version is 91Ω per pin. I brought the capacitor even closer which should reduce ringing further, but I can't verify because my scope is 200MHz and all I see is a flat line.

https://www.eevblog.com/forum/testgear/fast-rise-time-2ns-or-1ns-signal-generator/msg564319/#msg564319

[Qmavam]

 I bought an inexpensive Time domain Reflector based on a SN74AC14N.
https://tinyurl.com/rnz6aag

 I had installed a BOG antenna, (Beverage on Ground), it has been a few years, but I recall the impedance was high, so I modified the output resistor to get the reflectance bump to a larger difference, making it easier to measure.  I don't recall, the measurement, but I just checked and the output impedance is 575 ohms.
 So I like your idea of variable resistors.
When I did this I dragged my scope and extension cords out in the field to use. I'll be doing it again, my BOG area got cleared after a hurricane, backhoes and bulldozers cleared the area of trees along with all my BOG. I could have saved some of it, but had to much going on with home repairs.                       Mikek