APRS Interference on 144.240Mhz

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joseb
Posts: 5
Joined: Sun Jun 12, 2016 3:45 am

APRS Interference on 144.240Mhz

Postby joseb » Sun Mar 17, 2019 1:58 pm

I use my SDRplay and SDRUno software to monitor among other things 2 meter SSB (Upper Sideband -144.240Mhz). The problem that the APRS signal on 144.390Mhz comes on (1 second) and interrupts my listening on 144.240mhz. How do I filter out this interference? What happens is that the APRS comes on and deadens, lowers the receive on anything on 144.240Mhz.
Last edited by joseb on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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glovisol
Posts: 393
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: APRS Interference on 144.240Mhz

Postby glovisol » Mon Mar 18, 2019 8:18 am

This probably happens because the IF AGC is strongly driven by the APRS signal and quickly lowers the gain. This problem should be overcomed with the new IF AGC implementation of SDRplay. You should install Ver. 1.3 and verify the improvement. Pse post your result!

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g1hbe
Posts: 429
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: APRS Interference on 144.240Mhz

Postby g1hbe » Mon Mar 18, 2019 10:48 am

It's also a good thing to use as little RF gain as possible, rather than going for max. This will reduce the effect of strong local signals. Another way is to choose a small RF bandwidth (low sample rate) so that the interfering signal is off-screen and outside the IF b/w.
As Glovisol says, the new software is supposed to reduce this effect.

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Andy

joseb
Posts: 5
Joined: Sun Jun 12, 2016 3:45 am

Re: APRS Interference on 144.240Mhz

Postby joseb » Mon Mar 18, 2019 11:37 pm

I lowered the RF Gain and it did improve things a lot. The APRS still dampens the receive, but not as much as before.
Last edited by joseb on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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glovisol
Posts: 393
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: APRS Interference on 144.240Mhz

Postby glovisol » Tue Mar 19, 2019 3:30 pm

joseb, glad that things improved considerably, but you forgot to mention if you were using the new SDrplay Ver. 1.3 or older versions...

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