[op25-dev] rx.py Airspy MASTER GAIN Setting option?????

wllmbecks at gmail.com wllmbecks at gmail.com
Sun Sep 6 14:45:48 UTC 2020

Setting the manual gain mode in op25 will take away AGC and more importantly will
remove the false spike in the center of the spectrum.   This is quite so that you can visualize
the "Real" control channel from a figment of the Airspy's imagination.    

Note that a full reboot or removal and re-plugging of the SDR into the USB port will be
required to clear the Airspy from previous linearity or sensitivity modes.   Changing of the
rx.py command line arguments and restarting rx.py will not clear the internal registers of
the device, something that it took me a while to figure out.  

I would still recommend starting with (-q 0) while checking for the presence of TSBK's
coming from the control channel, and/or verification of a legitimate p25 signal by observing
the constellation or symbols plots.    But I think you'll be ok in using FFT once you have the
AGC gain modes disabled.

Please let us know how you make out.  Good luck!


-----Original Message-----
From: op25-dev <op25-dev-bounces at lists.osmocom.org> On Behalf Of op25 at zellners.com
Sent: Sunday, September 6, 2020 9:29 AM
To: op25-dev at lists.osmocom.org
Subject: Re: [op25-dev] rx.py Airspy MASTER GAIN Setting option?????

Quoting wllmbecks at gmail.com:

> The yellow highlighted text below in my rx.py command line is an 
> example of how my R2 device was set to manual gain mode whereby the 
> device responds to user specified LNA, MIX,
> and IF gain settings.
> ./rx.py --args "airspy=0,sensitivity=0,linearity=0,bias=0" -N 
> 'LNA:15,MIX:15,IF:10' -S 2500000 -T trunk.tsv ………

Thanks... I think that may be the  
magic,airspy=0,sensitivity=0,linearity=0,bias=0, as those names are  
present in the other program, but hmm... I would expect since I nuked  
them in that program it would persist? I guess not..

I will try this during some tests today... have to work on a more  
mission critical option at first.


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