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

wllmbecks at gmail.com wllmbecks at gmail.com
Sat Sep 5 13:29:51 UTC 2020



Graham Norbury dug into the Airspy library sometime back and came up with a fix to enable/disable the various gain modes.   I want to recall that he patched some of the existing code

to allow additional args to control these gain modes.   So it’s likely the following will only apply to the boatbod version of op25.   


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 ………





From: op25-dev <op25-dev-bounces at lists.osmocom.org> On Behalf Of Graham Norbury
Sent: Saturday, September 5, 2020 7:25 AM
To: op25-dev at lists.osmocom.org
Subject: Re: [op25-dev] rx.py Airspy MASTER GAIN Setting option?????


This happens when the agc is turned on.  Bill Becks and I experimented with it a while back and found a way to enable/disable, but at this moment I don't recall the magic incantation.




On Sat, Sep 5, 2020, 7:23 AM <op25 at zellners.com <mailto:op25 at zellners.com> > wrote:

Quoting Graham Norbury <gnorbury at bondcar.com <mailto:gnorbury at bondcar.com> >:

> I'm not aware of a master gain parameter.   LNA, MIX, IF are the three gain
> controls.  All take value between 0-15.
>> ./rx.py --args 'airspy' -N 'IF:10,MIX:5,LNA:15' -S 2500000 -f
>> 774.55625e6 -v 7 -T P25PC.tsv -q 2 -V -2  -U -x 2 2>> airspy.log

I reran my tests on this again, using -N 'IF:,MIX:,LNA:' like above  
with 0-15 values.

The spike for the CC, as a test, didn't budge at all, all 15, or  
anything in between, no changes.

It is significantly lower to start -20 to -40db lower v. other  
programs and depending on antenna.

Its almost like the gains are set to 0 or something and never  
change??? ? ? ? ?

Even using a duck direct to the Airspy with another program results in  
much higher signals on its spectrum, and gains will adjust accordingly.

Changes will occur in another program with adjustments to all 3  
(outside its faked single slider mode, using just the REAL GAINS),  
gains shows changes in the signals and noise floor.

In op25, not a bit of change at all in any thing. noise or signal.  
Like these are not being sent? Or not taking affect?? ? ? 15 for all,  
combos of values, even things like 50 for all three, no changes.

I am not sure what to even try at this point? Other than missing lib  
when it was compiled??? I didn't have the airspy then or airspy  
pacakges installed when compiled.. does that change anything??? It  
seems to work regardless of that, it tunes, it will trunk, voice etc.,  
just the gains don't seem to do a thing at all. IF there was something  
missing in this, I would expect it to fail to tune, audio etc..


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