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amdx
Guest

Thu Apr 30, 2020 3:45 pm   



I bought this TDR a few years ago,
> https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4
I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.
What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)
It a 50 ohm output impedance, I temporarily modified mine for 500 ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek

Jeroen Belleman
Guest

Thu Apr 30, 2020 3:45 pm   



On 2020-04-30 16:31, amdx wrote:
Quote:
I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4

I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.
What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)
It a 50 ohm output impedance, I temporarily modified mine for 500 ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek


What's the timebase setting on your scope? With a 12ft coax,
the reflection gets back after about 40ns.

Jeroen Belleman

George Herold
Guest

Thu Apr 30, 2020 5:45 pm   



On Thursday, April 30, 2020 at 10:31:55 AM UTC-4, amdx wrote:
Quote:
I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4
I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.
What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)

Open versus a short should give two very different reflections.
GH

Quote:
It a 50 ohm output impedance, I temporarily modified mine for 500 ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek



Guest

Thu Apr 30, 2020 5:45 pm   



On Thu, 30 Apr 2020 16:38:17 +0200, Jeroen Belleman
<jeroen_at_nospam.please> wrote:

Quote:
On 2020-04-30 16:31, amdx wrote:
I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4

I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.
What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)
It a 50 ohm output impedance, I temporarily modified mine for 500 ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek

What's the timebase setting on your scope? With a 12ft coax,
the reflection gets back after about 40ns.

Jeroen Belleman


If he's using a slow scope, a capacitor will make a slow "step", an
exponential actually. He could try 1 uF, for a 50 us time constant.

I use TDR to measure small Cs and Ls and ESRs, and see semiconductor
wire bonds and junction capacitances.

(Can't reply to original post for some reason.)



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

amdx
Guest

Thu Apr 30, 2020 6:45 pm   



On 4/30/2020 11:59 AM, Joerg wrote:
Quote:
On 2020-04-30 07:31, amdx wrote:
  I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4


  I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
  So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to  work! Both have a nice square wave
output.
  I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.


Ahm, please don't hit me for saying, but you did not accidentally have
the bandwidth limit engaged on the scope channel?


  What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)


Won't work, it has to be a cable.


  It a 50 ohm output impedance, I temporarily modified mine for 500 ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

                                    Mikek



Time was my problem, After Jeroen's post I new time was my error, I
first used delayed sweep to expand the edge. That found the step. Then I
triggered properly and just used a 0.2 us time base to see the step. it
saw 50 ohms for abut 320ft and then the open.
Joerg, worth asking, but, I fixed that at the start.
Thanks Guys.

Cursitor Doom
Guest

Thu Apr 30, 2020 6:45 pm   



On Thu, 30 Apr 2020 16:38:17 +0200, Jeroen Belleman wrote:

Quote:

What's the timebase setting on your scope? With a 12ft coax,
the reflection gets back after about 40ns.


The time interval will be different for different types of coax, though.
He needs to know what the transmission coefficient for his particular
coax is.

Joerg
Guest

Thu Apr 30, 2020 6:45 pm   



On 2020-04-30 10:08, amdx wrote:
Quote:
On 4/30/2020 11:59 AM, Joerg wrote:
On 2020-04-30 07:31, amdx wrote:
I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4


I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.


Ahm, please don't hit me for saying, but you did not accidentally have
the bandwidth limit engaged on the scope channel?


What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)


Won't work, it has to be a cable.


It a 50 ohm output impedance, I temporarily modified mine for 500 ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek



Time was my problem, After Jeroen's post I new time was my error, I
first used delayed sweep to expand the edge. That found the step. Then I
triggered properly and just used a 0.2 us time base to see the step. it
saw 50 ohms for abut 320ft and then the open.
Joerg, worth asking, but, I fixed that at the start.
Thanks Guys.


Good! I once became very frustrated because a delayed-trigger setup just
didn't show what I was expecting. Until I found out that the little
plastic (!) delayed-trigger clutch inside the otherwise very expensive
Tektronix scope had quietly broken off.

--
Regards, Joerg

http://www.analogconsultants.com/

Joerg
Guest

Thu Apr 30, 2020 6:45 pm   



On 2020-04-30 07:31, amdx wrote:
Quote:
I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4

I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.


Ahm, please don't hit me for saying, but you did not accidentally have
the bandwidth limit engaged on the scope channel?


Quote:
What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)


Won't work, it has to be a cable.


Quote:
It a 50 ohm output impedance, I temporarily modified mine for 500 ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek


--
Regards, Joerg

http://www.analogconsultants.com/

Joerg
Guest

Thu Apr 30, 2020 11:45 pm   



On 2020-04-30 15:15, Phil Hobbs wrote:
Quote:
On 2020-04-30 13:29, Joerg wrote:
On 2020-04-30 10:08, amdx wrote:
On 4/30/2020 11:59 AM, Joerg wrote:
On 2020-04-30 07:31, amdx wrote:
I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4



I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square
wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.


Ahm, please don't hit me for saying, but you did not accidentally have
the bandwidth limit engaged on the scope channel?


What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)


Won't work, it has to be a cable.


It a 50 ohm output impedance, I temporarily modified mine for 500
ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek



Time was my problem, After Jeroen's post I new time was my error, I
first used delayed sweep to expand the edge. That found the step. Then I
triggered properly and just used a 0.2 us time base to see the step. it
saw 50 ohms for abut 320ft and then the open.
Joerg, worth asking, but, I fixed that at the start.
Thanks Guys.


Good! I once became very frustrated because a delayed-trigger setup
just didn't show what I was expecting. Until I found out that the
little plastic (!) delayed-trigger clutch inside the otherwise very
expensive Tektronix scope had quietly broken off.


A 485, right?


No, AFAIR it was a Tektronix 2465. To my surprise there was a guy in
Greece who made new knobs and other mechanical parts for these. Shipping
to the US was pricey but afterwards the scope felt great. That was
before 3D printing, he had made molds for all that.

Whenever a client doesn't have a fast analog scope but needs one (and
they usually do) I recommend these. Just not a version with a digital
meter built in because those tend to overheat.

--
Regards, Joerg

http://www.analogconsultants.com/

Phil Hobbs
Guest

Thu Apr 30, 2020 11:45 pm   



On 2020-04-30 13:29, Joerg wrote:
Quote:
On 2020-04-30 10:08, amdx wrote:
On 4/30/2020 11:59 AM, Joerg wrote:
On 2020-04-30 07:31, amdx wrote:
  I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4



  I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
  So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to  work! Both have a nice square
wave
output.
  I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.


Ahm, please don't hit me for saying, but you did not accidentally have
the bandwidth limit engaged on the scope channel?


  What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)


Won't work, it has to be a cable.


  It a 50 ohm output impedance, I temporarily modified mine for 500
ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

                                    Mikek



  Time was my problem, After Jeroen's post I new time was my error, I
first used delayed sweep to expand the edge. That found the step. Then I
triggered properly and just used a 0.2 us time base to see the step. it
saw 50 ohms for abut 320ft and then the open.
  Joerg, worth asking, but, I fixed that at the start.
                                     Thanks Guys.


Good! I once became very frustrated because a delayed-trigger setup just
didn't show what I was expecting. Until I found out that the little
plastic (!) delayed-trigger clutch inside the otherwise very expensive
Tektronix scope had quietly broken off.


A 485, right?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

John Larkin
Guest

Fri May 01, 2020 12:45 am   



On Thu, 30 Apr 2020 15:29:30 -0700, Joerg <news_at_analogconsultants.com>
wrote:

Quote:
On 2020-04-30 15:15, Phil Hobbs wrote:
On 2020-04-30 13:29, Joerg wrote:
On 2020-04-30 10:08, amdx wrote:
On 4/30/2020 11:59 AM, Joerg wrote:
On 2020-04-30 07:31, amdx wrote:
I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4



I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but can't
get a step in the waveform, with an open cable on it.
So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to work! Both have a nice square
wave
output.
I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.


Ahm, please don't hit me for saying, but you did not accidentally have
the bandwidth limit engaged on the scope channel?


What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)


Won't work, it has to be a cable.


It a 50 ohm output impedance, I temporarily modified mine for 500
ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

Mikek



Time was my problem, After Jeroen's post I new time was my error, I
first used delayed sweep to expand the edge. That found the step. Then I
triggered properly and just used a 0.2 us time base to see the step. it
saw 50 ohms for abut 320ft and then the open.
Joerg, worth asking, but, I fixed that at the start.
Thanks Guys.


Good! I once became very frustrated because a delayed-trigger setup
just didn't show what I was expecting. Until I found out that the
little plastic (!) delayed-trigger clutch inside the otherwise very
expensive Tektronix scope had quietly broken off.


A 485, right?


No, AFAIR it was a Tektronix 2465. To my surprise there was a guy in
Greece who made new knobs and other mechanical parts for these. Shipping
to the US was pricey but afterwards the scope felt great. That was
before 3D printing, he had made molds for all that.

Whenever a client doesn't have a fast analog scope but needs one (and
they usually do) I recommend these. Just not a version with a digital
meter built in because those tend to overheat.


One of these?

https://www.dropbox.com/s/yguw683xfd04uki/ondo.gif?raw=1


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Clifford Heath
Guest

Fri May 01, 2020 1:45 am   



On 1/5/20 8:29 am, Joerg wrote:
Quote:
On 2020-04-30 15:15, Phil Hobbs wrote:
On 2020-04-30 13:29, Joerg wrote:
Good! I once became very frustrated because a delayed-trigger setup
just didn't show what I was expecting. Until I found out that the
little plastic (!) delayed-trigger clutch inside the otherwise very
expensive Tektronix scope had quietly broken off.
A 485, right?


No, AFAIR it was a Tektronix 2465. To my surprise there was a guy in
Greece who made new knobs and other mechanical parts for these. Shipping
to the US was pricey but afterwards the scope felt great. That was
before 3D printing, he had made molds for all that.


Speaking of broken knobs, I have a Tek 7904 with a 7a26 (400 MHz dual
vertical) and the volts/div knob is broken - 3/4 of the knob is missing.
Still usable, but I'd like to fix it.

I've searched, but not found any print files to 3D print a new knob. Any
hints on where to look?

It will need disassembly, as the calibration knob is also gone and the
end of that shaft is broken off.

Clifford Heath

amdx
Guest

Fri May 01, 2020 1:45 am   



On 4/30/2020 5:29 PM, Joerg wrote:
Quote:
On 2020-04-30 15:15, Phil Hobbs wrote:
On 2020-04-30 13:29, Joerg wrote:
On 2020-04-30 10:08, amdx wrote:
On 4/30/2020 11:59 AM, Joerg wrote:
On 2020-04-30 07:31, amdx wrote:
  I bought this TDR a few years ago,
https://www.ebay.com/itm/TDR-Time-Domain-Reflectometer-Fast-Clock-Version-Detect-cable-faults-More/152587007700?hash=item2386e4f6d4




  I used it on on a long wire on the ground to calculate the antenna
surge impedance, I saw a nice step in the trace, it worked fine.
Now my buddy bought one, and has a square wave on the scope, but
can't
get a step in the waveform, with an open cable on it.
  So he ask me to take it home and test it. I can't get it to work
either, and now, I can't get mine to  work! Both have a nice square
wave
output.
  I put a 12 ft coax cable on it without any termination, no step.
I put a long (100ft?) coax, that is wound on a spool, I get a small
dot like it is a very short step, but hardly noticeable.


Ahm, please don't hit me for saying, but you did not accidentally have
the bandwidth limit engaged on the scope channel?


  What can I hang on the output that will show a definite step or
any waveform just to show it works. (C, L, LC, RL ??)


Won't work, it has to be a cable.


  It a 50 ohm output impedance, I temporarily modified mine for 500
ohms
output for testing a high impedance antenna, had a step at 50% of the
voltage.

                                    Mikek



  Time was my problem, After Jeroen's post I new time was my error, I
first used delayed sweep to expand the edge. That found the step.
Then I
triggered properly and just used a 0.2 us time base to see the step. it
saw 50 ohms for abut 320ft and then the open.
  Joerg, worth asking, but, I fixed that at the start.
                                     Thanks Guys.


Good! I once became very frustrated because a delayed-trigger setup
just didn't show what I was expecting. Until I found out that the
little plastic (!) delayed-trigger clutch inside the otherwise very
expensive Tektronix scope had quietly broken off.


A 485, right?


No, AFAIR it was a Tektronix 2465.


That's a coincidence! That is the scope I'm using for the TDR. Except it's a
Tektronix 2465CTS model.
Mikek

Bill Sloman
Guest

Fri May 01, 2020 4:45 am   



On Friday, May 1, 2020 at 3:25:02 AM UTC+10, Cursitor Doom wrote:
Quote:
On Thu, 30 Apr 2020 16:38:17 +0200, Jeroen Belleman wrote:


What's the timebase setting on your scope? With a 12ft coax,
the reflection gets back after about 40ns.

The time interval will be different for different types of coax, though.
He needs to know what the transmission coefficient for his particular
coax is.


The time interval will be different for different lengths of coax. Long coax cable with a lossy dielectric will kill the high frequency components that make the visible step, but that would be the only issue. Cursitor Doom seems to be a rather low-end hobbyist.

--
Bill Sloman, Sydney


Guest

Fri May 01, 2020 4:45 am   



On Thu, 30 Apr 2020 17:24:56 -0000 (UTC), Cursitor Doom
<cd_at_not4mail.com> wrote:

Quote:
On Thu, 30 Apr 2020 16:38:17 +0200, Jeroen Belleman wrote:


What's the timebase setting on your scope? With a 12ft coax,
the reflection gets back after about 40ns.

The time interval will be different for different types of coax, though.
He needs to know what the transmission coefficient for his particular
coax is.


Most coaxial cables have insulator dielectric constants K in the 2.2
sort of range, so the velocity is c/sqrt(2.2) ish, around 2/3 the
speed of light, a little higher for foamed dielectrics.

Fun extremes are air lines (K=1, v=c) and coaxial ceramic resonators,
K in the thousands.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

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