SDRPlay overload "issue" on FM band

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DaveB
Posts: 129
Joined: Sun Feb 01, 2015 6:04 pm

SDRPlay overload "issue" on FM band

Postby DaveB » Sat Mar 07, 2015 7:30 pm

For info:
Beaming west - which is unusual - I've suceeded in overloading the SDR and generating inter-modulation products out of band. A number of input signals would have been above 70 dB and my set up includes a 20+dB preamp which is probably delivering 16dB extra after signal splitting. AGC was on. The problem was overcome simply by reducing the LNA GR to ensure the LNA did not kick in. Careful checking showed no reduction in s/n ratio on weak signals (because of the external preamp).

So - don't panic - but something to bear in mind to ensure best performance under different circumstances.

Rgds

David

DaveB
Posts: 129
Joined: Sun Feb 01, 2015 6:04 pm

Re: SDRPlay overload "issue" on FM band

Postby DaveB » Tue Mar 10, 2015 10:02 pm

I've been trying this out a bit more and have replicated the 'problem'. So may I suggest for the next release of the HDSDR plug-in that a tick box option be given for the LNA to be off manually. I suspect the problem is mixer overload with 20dB+ from a masthead preamp +19dB internal pre-amp in front of the Mirics tuner when there are multiple strong signals present. It would make it easier to disable the LNA than manually inputting a zero. You could leave the GR threshold at a sensible level for normal operation and just tick the box to turn it off if needs be.

David


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