I didn't pay particular attention to the original post but a (-q 2) would really be
unheard of with an Airspy device
unless it is way out of calibration. I suspect that the spike you're seeing in is not
a "real' signal.
Although it's hard to reproduce on demand, I have run into conditions where my FFT
plot displayed a spike at the
center of the spectrum that turned out to be false signal. Removing the antenna and
setting the LNA and Mixer gain
controls to zero made no difference in the amplitude of the spike at the center of the
spectrum.
As a suggestion, retest rx.py using (-q 0) as a starting point but add (-X) to let op25
try to resolve tuning errors to
see if you're actually getting a live signal, and check to see that op25 indicates
it's decoding trunk signaling blocks
and live traffic.
Raising and lowering LNA, MIXER, and IF gains should result in varying signal amplitude as
observed in the FFT plot
Typically, on my Airspy devices the IF gain maxes out at about a setting of 8-10 as far as
increasing signal amplitude
and whereby increasing IF gain only serves to raise the apparent noise floor and sometimes
introducing unwanted
IM products. But LNA and MIXER gains should play a very significant role in the signal
level as observed in the FFT plot
screen.
Bill
-----Original Message-----
From: op25-dev <op25-dev-bounces(a)lists.osmocom.org> On Behalf Of op25(a)zellners.com
Sent: Saturday, September 5, 2020 6:23 AM
To: op25-dev(a)lists.osmocom.org
Subject: Re: [op25-dev] rx.py Airspy MASTER GAIN Setting option?????
Quoting Graham Norbury <gnorbury(a)bondcar.com>om>:
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..
Ideas?????