Trouble making my low end TDR work, Help.

[amdx]

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]

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

 

[George Herold]

On Thursday, April 30, 2020 at 10:31:55 AM UTC-4, 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 ??)

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

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

 

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

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

 

[Joerg]

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

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

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.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Cursitor Doom]

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.

 

[amdx]

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.

 

[Joerg]

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.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Phil Hobbs]

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?

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]

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

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

 

[amdx]

On 4/30/2020 5:29 PM, Joerg wrote:

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

 

[Clifford Heath]

On 1/5/20 8:29 am, Joerg wrote:

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

 

[Bill Sloman]

On Friday, May 1, 2020 at 3:25:02 AM UTC+10, Cursitor Doom wrote:

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

 

On Thu, 30 Apr 2020 17:24:56 -0000 (UTC), Cursitor Doom
<cd@not4mail.com> wrote:

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

 

[Phil Hobbs]

On 2020-04-30 18:29, Joerg wrote:

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.

I have a 2467 (350 MHz, microchannel plate CRT) that I use occasionally.
It's a beautiful thing, but life has passed it by except when its
gloriously precise triggering is needed.

At IBM my daily driver was a 2465B, but these days I generally use
DSOs--TDS94C or TDS784A.

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]

On Thu, 30 Apr 2020 15:55:36 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

On Thu, 30 Apr 2020 15:29:30 -0700, Joerg <news@analogconsultants.com
wrote:

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

That is, incidentally, an equivalent-time-sampling oscillograph.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

[Joerg]

On 2020-04-30 16:46, amdx wrote:
> On 4/30/2020 5:29 PM, Joerg wrote:

[...]

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

The 2465 is among the best analog scopes money can buy these days. I
don't know what'll happen when they aren't readily available on EBay
anymore one day.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

On 2020-04-30 17:00, Clifford Heath wrote:

On 1/5/20 8:29 am, Joerg wrote:
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.

Maybe ask guys that sell knob sets for other Tektronix series? They
might know the market.

https://www.ebay.com/itm/Lot-of-20-Tektronix-Oscilloscope-Knobs-Type-500-Series/324148242863

It's been too long ago and I can't find the Greek guy anymore who sold
us the 2465 knob set.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Carl]

"Joerg" wrote in message news:hh60cfF3ebU1@mid.individual.net...

On 2020-04-30 17:00, Clifford Heath wrote:
On 1/5/20 8:29 am, Joerg wrote:
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.


Maybe ask guys that sell knob sets for other Tektronix series? They might
know the market.

https://www.ebay.com/itm/Lot-of-20-Tektronix-Oscilloscope-Knobs-Type-500-Series/324148242863

It's been too long ago and I can't find the Greek guy anymore who sold us
the 2465 knob set.

If you have a matching knob or the pieces to glue the busted knob back
together you can make a polyurethane rubber mold from that, and then cast as
many polyurethane plastic copies as you want. My favorite source is
www.smooth-on.com. I've used their Reoflex stuff to make a few small molds,
and cast rigid parts from their Smooth0Cast resin. I'd suggest a 30A or 40A
rubber for the mold and a 70D hardness resin for the knob. They have color
pigments for the resin so you can make a nice red knob , and lots of
great tutorial videos on their site. Email or call them for advice. They
have always been very helpful and knowledgeable when I've needed it. Not
counting time spent down the rabbit hole of watching their videos , it
should take you maybe an hour to make and pour your first mold and after an
overnight cure and a few minutes for demolding and cleaning you should be
able to get your first knob cast in less than 30 minutes. Biggest downside
is that their small test kits are about $30 each, so $60ish plus mold
release for one knob but you will have plenty of material left over.

--
Regards,
Carl Ijames