# Re: Feed Line Loss @ Freq vs. Price

• Subject: [amsat-bb] Re: Feed Line Loss @ Freq vs. Price
• From: "i8cvs" <domenico.i8cvs@xxxxxx>
• Date: Fri, 11 May 2007 04:21:46 +0200

```----- Original Message -----
From: "Stargate" <stargatesg1@verizon.net>
To: <amsat-bb@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
system
> up and
> running to give me a base line for future improvements.
>
> Any thoughts?
>
> Thanks.
> RoD
> KD0XX

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) ]
10

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

Example:

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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