DSDPlus How to Adjust LNA, MIX, and IF Gain on Airspy R2 with DSD+ Fastlane

[wagros]

Hi everyone,

I’m using an Airspy R2 together with DSD+ Fastlane, but I’m still not sure how to properly set the LNA, MIX, and IF gain levels.
I never know which one to start with or how far to increase each control before it becomes too much. 😅

If anyone could share some general guidelines or example settings that work well for you, I’d really appreciate it.

73!

 

[wgbecks]

Hi everyone,

I’m using an Airspy R2 together with DSD+ Fastlane, but I’m still not sure how to properly set the LNA, MIX, and IF gain levels.

Running fmpa.exe -h will provide you all of the command line arguments in addition to keyboard inputs necessary to adjust these gain value on the fly. Unless you have very strong neary signals, you can use those shown in my fmpa-cc.bat (below) that shoud work well for you.

start C:\dsdplus\FMPA -rc -i1 -o20001 -L15 -M12 -V8 -v100 -b12.5 -n1 -f853.925 -_3

Using the above values, adjust LNA as necessary to obtain enought gain to support reliable decoding. LNA-15 is full gain that may have
to be reduced under specific conditions to prevent SDR overload to control the noise floor and the generation of signal artifacts. Mixer
and IF gains are generally optimum as seen in my example. It may be necessary to reduce Mixer along with LNA when you're dealing with
very strong localized signals.

FMPA Spectrum (FFT) of a nearby (7-miles) P25 TRS Control Channel.

 

[wagros]

I was hoping there’d be some kind of “recipe” for this setup.
The best results I’ve managed so far are with the settings shown in the screenshot.
Appreciate you sharing your config in the thread — it definitely helped me get closer to a good balance!

 

[wgbecks]

I was hoping there’d be some kind of “recipe” for this setup.
The best results I’ve managed so far are with the settings shown in the screenshot.
Appreciate you sharing your config in the thread — it definitely helped me get closer to a good balance!

View attachment 190927

It looks like you may be experiencing some form of interference based upon the concentration of signals (spikes) in the spectrum display.
WIth the tuned frequency redacted, I tell if it might be Digital TV, Cellular or LTE interference although the IF overlay looks like a pretty clean
replica of a P25 Control Channel. Are you having decoding errors? What does the Source Audio window look like? Do the spikes go away or deminish when reducing LNA gain to an even lower value?

 

[mtindor]

LNA: MIX: IF:

J/K/L (keyboard adjustments)

I have a dozen Airspys all over. We run them all at LNA:15, MIX:15 and simply adjust IF: (L, shift-L) depending upon whether it's getting oversaturated from strong signals or not. Of course the keyboard commands only work when you are "focused" on FMPA.exe

And I disagree with @wgbecks. You're signals look clean. You just have a ton of signals to observe. I don't see any overloading or interference.

Mike

 

[wagros]

LNA: MIX: IF:

J/K/L (keyboard adjustments)

I have a dozen Airspys all over. We run them all at LNA:15, MIX:15 and simply adjust IF: (L, shift-L) depending upon whether it's getting oversaturated from strong signals or not. Of course the keyboard commands only work when you are "focused" on FMPA.exe

And I disagree with @wgbecks. You're signals look clean. You just have a ton of signals to observe. I don't see any overloading or interference.

Mike

Ok, Mike, thanks for your tip.

I actually have plenty of signals in my area, but the most interesting ones — like police and fire — are encrypted.

Even so, scanning is still a lot of fun!