LNA settings for op25

[Dufus]

How do I determine the best value for LNA:? I've tried different values and don't really see a difference but do not really know what I should be looking for.

I'm using RPI3b, flightaware pro dongle, external usb power, for dongle-kb-mouse, small hdmi tv w/audio, and an external discone antenna. The sites are like 30 miles away, one is 774.+- and the other is 851.+- (Hancock Co, Ms.)

I get a sharp chirp in the audio and trying to tweak my startup commands to maybe lessen the chirps.

right now I'm using
./rx.py --args "rtl=0" --gains lan:47 -q 0 -S 960000 -n -w -U -T trunk.tsv -2 -v5 2>stderr.2


TIA

 

[boatbod]

As LNA gain increases, so does the noise floor. You can use osmocom_fft utility to experiment with gain values and dynamically see their effect on both the signal and the noise floor. Raise the LNA setting just enough to bring the signal peak up while leaving the noise floor almost unchanged.

Chirps in the audio are usually related to PCM underruns. On a rpi3 reducing your RTL sample size to the bare minimum (57600) to minimize cpu impact will likely have the biggest net gain.

 

[Dufus]

thanks

Got a little yagi directional antenna put up today, that also helped a lot.

-S 57600 did greatly reduce the chirps. thanks again.