Military Air monitoring

[MARKB911Participant]

Hello All,

I new to the forum, but have had an RSP1 for about 18 months and am very happy with it overall. One thing I have been struggling with is that I am getting very strong FM radio images over large swaths of the Military Airband (225-400MHz). I have read old posts about using the FM notch filter to knock the interference down, but I don’t see a reference to this filter in the current manual or in the software itself.
Can anyone provide some guidance?

Much Thanks,
Mark
Buena Park (Near Los Angeles), California, USA

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   SDRPlay-milair.jpg
   

[Andy2Participant]

IIRC, the original RSP1 did not have any notch filters. I think they appeared with the RSP2. Later models have FM, MW and DAB notches.

[MARKB911Participant]

Yep that’s probably it. I have an RSP1, not a 1A…..Time to upgrade, I guess!!!

[Andy2Participant]

You could try using a different ‘LO plan frequency’. On the small MAIN panel, select SETT. Then from the small window that opens, go to CAL and find ‘LO Plan Frequency’. It’ll be set to AUTO, but try selecting 144 instead, this has the effect of moving *some* images out of the way.

[MikeAgnerParticipant]

Assuming that you aren’t overdriving the SDR, an easy way to stop this problem is a FM bandstop filter. An example of one is here

http://www.parelectronics.com/fm-broadcast.php

Mike

[Author]

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