[App_rpt-users] Desense (Echo) on RTCM

Hayden Honeywood haydenph91 at gmail.com
Mon Sep 11 23:10:07 EDT 2017

Hi All,
Gotten around to finally installing one of my VOTER boards (RTCM) to Site 1.
All tested on the bench - the only thing I did not test was duplexing on
the bench as I had no spare duplexers.

Installed to the site - nothing changed from the duplexer patch cables
onwards to the antenna. Now I have what I assume is a huge amount of
desense. The previous repeater installed was the same model radio and
worked fine.

Disabled CTCSS encoding as the repeater would talk to itself echoing over
and over.
Attached is a sample audio recording, you can hear the growl of the audio
delay in the system.

I've been waiting to get back to the site (snow and time permitting), but
in the meantime thought I'd post here to see if anyone has had any similar
experience with desense and the RTCM's talking to themselves....

My second unit works on the bench, duplexing into a dummy load and antenna
fine. Measuring desense is tricky as the radios have been modified so they
don't have any external audio connections anymore, so the lid has to be
popped to connect the service monitor.

Next stop is to test the system into a dummy load at the site, if that
fails, then remove the system and replace with Site 2 equipment and test.
If it duplexs fine into a dummy load and not into a antenna, has anyone had
issues with RF maybe coming back down the GPS antenna cable? That is the
only physical external connection near the antenna we've changed from the
previous system.

Hayden VK7HH
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