Ping Joerg: doppler pencil probe

Can you TDR it?

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John Larkin Highland Technology Inc

jlarkin at highlandtechnology dot com

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators

I don't have access to a TDR. I suppose I could put 50 or 100 ohms in series to the TG and look at the voltage on a spectrum analyzer.

--sp

Mine are between 800pF and 900pF. This is for split-disk (CW) Doppler transducers of about 0.450" diameter, including 6ft cables. But the cable part won't matter if one side is matched to the cable impedance. Typically the system side.

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Regards, Joerg 

http://www.analogconsultants.com/

Okay, thanks!

Sounds like this one is open. I can hand it back as 'broken' with a clear conscience.

Bset regards,

Especially if they don't show any 8MHz resonance when on the analyzer or generator. Did you measure the other half? It's rare that both connections break.

--
Regards, Joerg 

http://www.analogconsultants.com/

The case is plastic, but I'll try to the shield tomorrow (and try the SA).

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward" 
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Flat as a pancake 5-10MHz on any pair of wires. It's dead, Jim.

I can TDR stuff for you, if you have time to ship it to me.

You can get an 11801+SD24 rig on ebay for under $2K. A very handy thing to have.

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

P.S.

Yup, that's been killed dead, as John Wayne would have put it.

--
Regards, Joerg 

http://www.analogconsultants.com/

You can actually do TDR with any scope that has a fast enough rise-time relative to the artifacts you are looking for on the cable, and a pulse generator that can produce a step output. Or, if you have a suitably narrow pulse that is not a step, you can interpret the results just a little differently. I have used this many times to figure out which end of a several-foot cable has the short.

Jon

Sure, but a real TDR/sampler has fraction of an inch resolution and cool time/distance/impedance readouts. Great for stuff like PCB traces and evaluating connectors.

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

A basic DCR bridge with a 10 turn pot as part of the bridge can give you the short location in a pair of conductors, as long as you have access to both ends of the pairs to test.

Looking for opens is a little more involved. That can be done in two ways that I know of, a TDR or a HV induced signal with in a DCR bridge, the arc serves as the shorting path point.

Jamie

Just measure the capacitance at each end.

--
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In grad school we* found a spool of coax with access to both ends. A pulse generator, scope, and any termination you can find.... lotsa fun.

George H.

*myself and a navy electronics tech, he was a bit older, but we got along just fine.

I'd love to learn how to 'fly' a TDR.

George H.

I'd love to learn how to 'fly' a TDR.

George H.

++++++++++++++++++++++++

Keep you eye out for a Tektronix 11801 with a SD-24 sampling head. It's a great TDR, not to mention a really fast scope. Bad ones show up on ebay from time to time for around $200 or so. Most of the time, the only thing wrong is bad memory batteries.

The SD-24 heads go for $2-400.

The only con is how big it is. But then it's less likely to get legs.

tm

Does anyone make fast TDRs anymore? I've been looking but everything I've found is intended to test cables. Unfortunately, eBay isn't possible.

Plenty of test equipment suppliers.

Is 7 ps fast enough?