Re: 7S12 TDR Cable


 

When I tried to send this last night at 7:51PM PST Yahoo rejected it. In
fact it seemed to have been rejecting emails for a few hours.
Dennis

-----Original Message-----
From: Dennis Tillman [mailto:@Dennis_Tillman_W7pF]
Sent: Monday, April 04, 2016 7:51 PM
To: 'TekScopes@...' <TekScopes@...>
Subject: FW: [TekScopes] 7S12 TDR Cable

Hi Nathan,
TDR is a fascinating world unto its own. There are many things you can do
with it but it is so unlike everything you probably know about electronics
that you will want to get some help. One great source is the Tektronix Time
Domain Reflectrometry Measurements book. It was written in 1970 but
everything in it is still current today.

It is interesting to note that the fastest TDR systems available today are
still only about 50% faster than the 7S12 /S-52 / S-6 system equivalent
risetime of ~30pSec. So, in other words it was an outstanding system in its
day, and it is an excellent system to have today.

Dennis Tillman W7PF

-----Original Message-----
Sent: Monday, April 04, 2016 7:36 AM
Subject: [TekScopes] 7S12 TDR Cable

One of my new scope acquisitions(currently in transit) is coming with a
7S12/S-6/S-52 TDR setup. Of course no cables. Right now I'm looking at the
S-6 manual and looking at the interconnection diagram. It looks like I
should be using the 750ps cable(015-1017-01) and the "Test Line" cable
015-0123-00. Obviously these cables all got lost, and I can't locate any at
the moment. I've saved my searches and will keep an eye out. I'm trying to
understand the requirements of a replacement.
As I understand this, the interconnect cable being of a certain electrical
length was to delay the pulse reaching the S-6 until after the trigger? So
that would be satisfied by anything that delayed at LEAST 750ps? I have some
6 inch RG-402 jumpers that using book figures for 402, should be around
780-820ps. Hoping that will work, as I don't have anything to measure the
exact electrical length of a cable... Until I get the TDR working. Go
figure.
The "Test Line" is specced at 1ns, and I assume that this was to make the
interconnection from "trusted test gear" to "circuit under test" a
fixed/known distance from the sampler as well as avoiding too short a cable
total/too short pulse+reflection? I'm thinking that once I get this working
I can use a "roughly 1ns" cable to attach another cable to the end, and trim
to 1ns?
Any idea what the tolerances would be on these cables from the factory?
Nathan KK4REY
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Posted by: Nathan Johnson <jdownj@...>
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