Quoting Graham Norbury gnorbury@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..

Ideas?????

If you're using rx.py try setting "--gain-mode 0" on the command line. That parameter is not implemented in multi_rx.py but if you change it in one app (e.g. gqrx), it will persist in other apps until you power cycle the airspy dongle.

Graham

On 9/5/20 8:25 AM, Graham Norbury wrote:

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.

Graham

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

Quoting Graham Norbury <gnorbury@bondcar.com
<mailto:gnorbury@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..

Ideas?????

Quoting wllmbecks@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.

Thanks....

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@lists.osmocom.org On Behalf Of op25@zellners.com Sent: Saturday, September 5, 2020 6:23 AM To: op25-dev@lists.osmocom.org Subject: Re: [op25-dev] rx.py Airspy MASTER GAIN Setting option?????

Quoting Graham Norbury gnorbury@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..

Ideas?????

A good tool is to take a look at your symbols and mixer plots to verify if the (-q 2) is the right prescription for your particular device. Start with (-q 0) and if you get TSBK's then let it run for five to ten minutes before checking the reported frequency error and then make your corrections accordingly.

However, I have run the calibration utility on all of my Airspy devices using a GPSDO as a stable and accurate frequency reference. In my case, the corrections added to the rx.py command line were (-q 0.1) & (-o 30) that results in an average frequency error of no more than 10-20 Hz as reported by op25.

Even though the R2's and Mini's are TCXO based, they are far from perfect and do drift the first five to ten minutes when starting up from cold. So, this has to be taken into consideration when running the calibration utility, or in making your PPM and offset corrections in op25.

Bill

-----Original Message----- From: op25-dev op25-dev-bounces@lists.osmocom.org On Behalf Of op25@zellners.com Sent: Sunday, September 6, 2020 11:33 AM To: op25-dev@lists.osmocom.org Subject: Re: [op25-dev] rx.py Airspy MASTER GAIN Setting option?????

Quoting wllmbecks@gmail.com:

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.

The -q 2 for PPM of 2, is based on another programs output of its auto ppm.

I will try with 0 as well. But with the 2 it was producing audio etc..

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.

This is not a spur, or anything of the like. Disconnect the antenna, its gone. I am not any sort of OP25 guru etc.... but lets just say this ain't my first rodeo in RF.... :) :) ;)

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.

Op25 does already indicate its a live signal, just 20-40db down. I get audio, TSBKS, using a -v10 I get the slew of decoded TSBK data, with an occasional CRC error. Which is related to the low signal.

I am also not working from a guess on the frequencies of the system(s). Lets just leave it at that I've got more knowledge about what frequencies and towers these things are using that a certain other site and the FCC does. :) ;) ;)

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

I think in another setup I am about 10-12 for LNA, and 8-7 on the IF and MIX as I recall. As I played to max signal and reduce the noise floor. I'll have to find my note on it.. its not on this box.

I think the other post to disable what ever those modes are is the key.. which when its reset, ie: powered off and moved to another box, my OP25 setups is not that box since op25 is not Python3 compatible, yet, and so I move it to the 18.04, with the ulitimate goal to possibly move it to a Pi(s), which I was hoping to dump, but there is a bug in another program to use them there. I am guessing the firmware of the AS's resets it to use these modes??? Where as the other program stores those settings and likely restores them when it sees the same tuner... as it does this with RTL's...

We'll see what the tests do with the magic disable commands....

You should be good to go if you have 10 MHz reference clock available. The Airspy's accept anything from 10 MHz to 100 MHz external clock reference on the MCX connector.

Don't ask me how the internals figure this out or if any configuration is necessary to specify the source reference. I haven't tried this but will go back to my shop and connect a 10 MHz reference to an R2 to see what if any affect it has on op25 receiving a live p25 system.

Bill

-----Original Message----- From: op25-dev op25-dev-bounces@lists.osmocom.org On Behalf Of op25@zellners.com Sent: Tuesday, September 8, 2020 10:05 AM To: op25-dev@lists.osmocom.org Subject: Re: [op25-dev] rx.py Airspy MASTER GAIN Setting option?????

Quoting wllmbecks@gmail.com:

A good tool is to take a look at your symbols and mixer plots to verify if the (-q 2) is the

Thats why I use OP25 for the constellation etc. that other software doesn't provide. More accurate to tune.

The 2 ppm is accurate as its confirmed with other programs. Which start with a 0 and over time it is steady at 2ppm +- a little...

However, I have run the calibration utility on all of my Airspy devices using a GPSDO

What is the CLKIN expecting? I'd have to check to see that our GPS simulcast controllers put out a similar or compatible signal... and I might drag one to a site when I go to test with...

But the -q 2 setting is accurate as anything or more less, and nothing decodes, nice tight constellation.

On Fri, Sep 4, 2020 at 11:10 AM wllmbecks@gmail.com wrote:

As Graham pointed out, there is no “Master” gain control built into the interface specification

of Airspy devices. However, In addition to manual gain control, there are sensitivity, and linearity modes

that apply AGC over the LNA and Mixer stages.

The “Master” gain control it seems is a feature in SDRTrunk whereby some values are applied to the

LNA, Mixer, and IF gains settings in addition to allow the end user input specific Tuner gain settings.

That said, there is no need to mimic overall RF amplitude values displayed on op25 FFT plots.

The fundamental difference between typical RTL SDR devices and the Airspy R2’s and Mini’s

is the much lower noise floor and the superior signal handling characteristics of the Airspy.

At the end of the day it’s all about Signal to Noise (S/N) performance of any given radio receiver

that defines overall usable sensitivity.

Shown below are FFT plots captured from the same P25 system with an Airspy R2 followed by

a NooElec SMArt. Observe the Airspy exhibits an average noise floor of approximately -80 while

the RTL exhibits an average noise floor of approximately -63 to -64 that clearly demonstrates

that the Airspy has a 16 to 17 dB advantage over the RTL device.

Er, no.. it means that *after all of the gains have been applied*, the noise floor measures differently. As you pointed out above, then apparently immediately forgot, it's SNR that matters. Eyeballing your plots, it seems like the SNR is similar - somewhere in the 35-40dB range (can't tell more than that, given the resolution). Note that the vertical scale is not the same between the two plots. Also, the RF frequency is not the same, so that's probably not a fair comparison either.

~iain

In addition to the lower noise performance, the signal handling in crowed RF spectrums

of the Airspy is also a plus. I happen to live in a rural area where there are few in-band 800 MHz

signals, but it should be noted that most RTL’s suffer from self-induced intermodulation interference

when operated in crowded RF spectrums.

*Airspy R2 ./rx.py --args 'airspy' -S 2500000 -N 'LNA:15,MIX:15,IF:10'*

*NooElec RTL** ./rx.py --args 'rtl' --gains 'lna:49'*

The third FFT plot below does demonstrate the relatively poor IM performance of an RTL SDR

captured from one of my remote instances of op25 tuned to a VHF P25 system where there

are numerous in-band signals. In this case I am using a five element Yagi antenna aimed at the

distant RFSS in combination with minimum LNA settings to mitigate as much of the IM products

as are possible.

Signals shown in the plot below approximately -45 are IM products and are not real in-band signals

when at times there are legitimate in-band signals that do produce IM products that cause bit errors

to the desired P25 control or voice channels.

*NooElec RTL** ./rx.py --args 'rtl' --gains 'lna:49'*

Bill

-----Original Message----- From: op25-dev op25-dev-bounces@lists.osmocom.org On Behalf Of op25@zellners.com Sent: Friday, September 4, 2020 5:35 AM To: op25-dev@lists.osmocom.org Subject: Re: [op25-dev] rx.py Airspy MASTER GAIN Setting option?????

Quoting Graham Norbury gnorbury@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.

Ummm...mmm...hmmmmmm...

SDRTrunk exposes:

4 CONTROLS and 3 options in a drop down.

A guess is these "modes" are some sort of custom setup? As you can set CUSTOM MODE and you can then adjust IF,MIX,LNA separately... in SENSITIVITY or LINEARITY MODES it has a "MASTER" slider which I will take it that if there really are only 3 real gains must be a custom adjust to all 3 via that slider???? Which it doesn't reflect in the GUI that its adjusting them.... but thats not really relevant here.

I am trying to match performance from an RTL to the Airspy, and the plot on the spectrum is at least 20db down from the RTL (RTL Gain 49)..unless the Airspys are significantly less sensitive which SDRT doesn't seem to show.

I get -20db power level with the RTL and and the airspy is at -40db...and playing with those gains didn't seem to budge it... hmmm..

I'll give another whack tonight using only the 3 controls and see what I get...

Thanks...