Tek has some very interesting TDRs out including
software controlled PHD (Push Here Dummy) models
for the 90's technician. He may not understand the
underlying principles, but he knows which button to
push to get the answer (which is usually given in a
PASS/FAIL mode). Ah, the "wizard"-ry of today's
technical world. I beleive these models start with
a W prefix. They are primarily 75-Ohm models
for the cable television world and have two pulses
for short and long distances. They can go through
splitters and show you both legs of the splitter's output.
Better than a spectrum analyzer and tracking generator,
of course (provided one has access to it), is a network analyzer
such as the HP 8711, 8712, or 8953 (I think that is the correct
model number). With such a device, you can "normalize" out the
connecting cables. Option 100 allows the 8711 and 8712 (not sure
about the other) to measure Structural Return Loss (SRL), a very
useful measurement.
73,
Bob AA0CY
----------
From: Stan or Patricia Griffiths[SMTP:w7ni@teleport.com]
Sent: Monday, August 30, 1999 7:43 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] BELDEN 9913 COAX PROBLEMS?
Ron Youvan wrote:
> Hi:
> << as we all know we can use our TDRs to find where the loss is located.
> Gosh, I
> forgot we don't have a TDR system. >>
> I have a Tektronix 1505, all I can measure is the surge impedance along the
> cable
> I find nothing in the IB about the `loss' of the cable.
>
> 73 (= Best Regards) de Ron ka4inm@qsl.net
> VISIT my HAM WEB SITE at: http://www.qsl.net/ka4inm
>
> Hi Ron,
I think you CAN determine cable loss with a TDR but takes some sophisticated
measuring
techniques to do it. BTW, what is a Tek 1505? I checked the 1999 Catalog and
still
see versions of the 1502 and 1503 but nothing about a 1505. Tek COULD have a
new
model that I don;t know about but I try to follow that industry pretty close.
My preferred method of measuring cable loss is to use a spectrum analyzer and a
tracking generator. (Yes, I have one that works up to 1.8 GHz.) This method
will draw
you a continuous graph of the loss from about 100 KHz right up to 1.8 GHz, and
then
plot it on paper for you. You need to have access to BOTH ends of the cable to
do this
correctly. If you have two runs of coax on your tower, you could connect them
together
at the top and find the total loss of both of them in series. Another approach
would
be to run a temporary "test cable" up your tower and connect it to the top end
of your
coax cables, one at a time. You could measure the total loss of your coax runs
plus
the loss of the "test cable" and subtract out the "test cable" loss leaving the
loss of
your coax runs.
Stan w7ni@teleport.com
>
>
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