[App_rpt-users] Desense (Echo) on RTCM

Tim Sawyer tisawyer at gmail.com
Tue Sep 12 00:10:33 EDT 2017

It does sound like your repeater is hearing itself. The delayed echo is
because of the jitter buffers required to stream audio. Normal repeater
trouble shooting methods apply. You have to figure out how the Tx RF is
getting into the Rx. I've never heard of the Rf coming down the GPS cable.
I suppose that's possible. But even if it was your receiver should be
shielded well enough to prevent the desense.

On Mon, Sep 11, 2017 at 8:10 PM, Hayden Honeywood <haydenph91 at gmail.com>

> 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.
> Regards
> Hayden VK7HH
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