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Re: Mode-S Desense

Hi Dennis,

One possibility is that something got bumped on the 70cm
uplink - a loose connection somewhere.  They make for great
non-linear elements, generating lots of harmonics.  I have
a significant desense problem from time to time, and have
tracked it down to a bad set of contacts on the polarization
switching relay on the 70cm antenna.  Sometimes all is quiet,
other times the noise floor rises so high it hits me in the
face when I transmit.  Flip the relay a few times, and the
noise level changes.

Before making any other changes, you might want to give the
uplink a quick once-over to be sure.


Greg  KO6TH

>From: dfk6mgm@postoffice.pacbell.net
>Reply-To: dfk6mgm@pacbell.net
>To: amsat-bb@AMSAT.Org
>Subject: [amsat-bb] Mode-S Desense
>Date: Fri, 29 Nov 2002 11:01:25 -0800
>I have recently replaced my mode-S dipole fed barbecue type grill
>antenna with helix fed offset dish. My problem is, that with the change,
>I am getting big desense on my FT 736 from the 70 Cm uplink. Never had
>this problem with the old grill antenna.
>The antenna configuration is:  7 Ft. fiberglass boom with a KLM 40CX on
>one end, a KLM 13C on the other end, with the offset dish in Th. middle.
>I have a D.E. primp mounted at the dish with the down converter in the
>shack about 35 ft away. The problem goes away when I kill power to the
>primp. (power fed via the coax).
>I have tried new coax and tried bonding and grounding on the new dish
>with negative results.
>I wonder if anyone been able to solve a similar problem?
>TNX, Dennis K6MGM
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