[amsat-bb] Re: Feed Line Loss @ Freq vs. Price

i8cvs domenico.i8cvs at tin.it
Thu May 10 19:21:46 PDT 2007

----- Original Message -----
From: "Stargate" <stargatesg1 at verizon.net>
To: <amsat-bb at amsat.org>
Sent: Thursday, May 10, 2007 11:26 PM
Subject: [amsat-bb] Re: Feed Line Loss @ Freq vs. Price

> While on this subject, has anyone used a "Return Loss Bridge" (RLB) to
> measure their actual
> total system loss. I was planning on doing that when I get my antenna
> up and
> running to give me a base line for future improvements.
> Any thoughts?
> Thanks.
> RoD

Hi Rod, KD0XX

Disconnect your coax cable from the antenna connector and short circuit 
the inner conductor with the outer conductor at your transmission line
output end.

Then using your RLB measure the Return Loss at the other end of the line
near your TX or RX and convert the measured Return Loss in dB to the
equivalent SWR

In this conditions the matched-line loss for the frequency of measurement
may then be determined from:

Lm (dB) = 10 log      [ (SWR+1) / (SWR-1) ]

Where SWR = the SWR value measured at the line input with the other
end shorted


If the measured return loss of your short-circuited line is 2.92 dB
corresponding to a SWR = 6  then the matched-line loss of your transmission
line at the frequency of measurement is Lm = 1.46 dB

Best 73" de

i8CVS Domenico

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