Message-ID: <000e01c0d20e$9103e2e0$766b1b3f@f3g6s4>
Reply-To: "dfs" <dfs@gateway.net>
Reply-To: lancair.list@olsusa.com
From: "dfs" <dfs@gateway.net>
To: "Lancair list" <lancair.list@olsusa.com>
Subject: Re: AVIONICS BLUES ...AGAIN
Date: Tue, 1 May 2001 00:15:50 -0700
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Concerning getting a VSWR test done on your airplane's antenna systems, a
good (emphasize GOOD) avionics shop should have the needed test sets to
measure the characteristics of your installations.

Back when my Lancair ws quite new, I was having a lot of Com troubles - a
lot of "Say again please, your transmission is nearly unreadable" from the
tower where I was based.

Went over to the avionics shop at the Long Beach, CA airport in the LA area,
(don't know if they are still there - they come and go these days) and got a
complete VSWR check-out of all my transmitting antennas. (The unit I had
originally built into my vertical stab for Com 1 was terrible - up to 4+:1 -
which explained my problem).

Jury rigging a Bob Archer com antenna behind the rear bulkhead (VSWR 1.4:1 -
worst case over the frequency range) cured my problem.

Incidentally, a way too high VSWR isn't just a transmit/receive problem,
when the reflected power becomes high enough, it is possible to fry your
radio's output stages, depending on the brand, it's age and other
miscellaneous things like that. Most GA radios are designed to operate with
some reasonable control of the installed VSWR.

Cheers,

Dan Schaefer


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