[TowerTalk] Evaluating coaxial cable not from a dealer

[Dave Hachadorian]

An antenna analyzer can give you an idea of the loss.

Hook the analyzer to one end of the cable, and leave the other end open.

Dial the analyzer up to 30 or 50 MHz.

Loss in dB = 10 log ((swr+1)/(swr-1))

Then, look up the specs for the cable in question and see how the observed 
loss compares to the specification loss for that frequency and that length.

This technique can also be used to evaluate loss in existing installations, 
even with an antenna attached.  Just dial the analyzer frequency to find a 
point of maximum SWR. At that point, the antenna is practically 
disconnected.


Dave Hachadorian, K6LL
Yuma, AZ



-----Original Message----- 
From: Steve K8JQ
Sent: Saturday, March 6, 2021 4:32 PM
To: TowerTalk
Subject: [TowerTalk] Evaluating coaxial cable not from a dealer

Occasionally someone will post here or on other amateur radio forums
coaxial cable for sale. Often unused, left over from a project, on a
reel, pickup only, as-is where-is, cash. If one were to pursue such a
purchase, what would one look for and/or do to validate that the cable
is good?

An eyeball physical inspection of the cable is an obvious thing to do.
One can see the outer layer of cable on the reel and perhaps both ends
of the cable. Is that enough?

Should one make some electrical tests before handing over the cash? What
tests and with what test equipment? A few spot frequencies? Wideband
sweeps? Antenna analyzer? VNA? Transmitter with power meter? Something
else? What would you do if both ends are not available or do not have
connectors?

Is it OK to transport a reel with a few hundred feet (or more) of cable
on its side or should the reel be "standing up" in the bed of a pickup
truck?

What else to look for, think about, consider?

Steve, K8JQ
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