Airspy Mini and 3 gains in GQRX

[Ronneil Camara]

Good morning/evening from Chicago. I have both rtlsdr dongle and airspy mini. I bought the airspy mini based on claims from people saying like "oh, the mini can really tune to the weak signals being overwhelmed by other stronger signals". Anyways, I think I expected too much from airpsy mini. I don't see much difference on the signal quality against rtlsdr dongle.

When I try to capture from NOAA weather, I set my sample rate to 3000000 and decimation to 32 so that I can filter signals I don't need. That's based from my understanding. I also read that when adjusting gains, have a high value in the gains doesn't really help. But the key is to get a good signal to noise ratio(SNR). Well, I've been trying to adjust LNA, MIX and IF so that when there is a NOAA(137+Mhz) satellite pass, the spike is like 30db+. I really don't know which of the 3 gains should be adjusted. I'm adjusting each gain everytime to learn how it displays the waterfall. I've tried LNA=11, MIX=5, IF=6 and waterfall is clean but image is noisy. Here is an example - https://imgur.com/a/2TkMM

However, there are cases that even if the satellite was very low, I get a decent image but I forgot what LNA, MIX or IF gain I set.

What is the ideal configuration of gqrx when using it with Airpsy mini?

Neil

[Alexandru Csete]

Hi Neil,

Setting MIX and IF around the middle, perhaps slightly above, then
adjusting LNA will probably work in most scenarios. Unfortunately,
gqrx does not implement the more convenient "sensitivity" and
"linearity" gain modes that would make this much simpler.

As for the image quality, gqrx may have some bugs with the NOAA APT
settings but I haven't had any time to investigate. Be sure to use the
"APT" deviation and wide enough filter. You can also try recording the
audio through a virtual audio interface, since the built-in recorder
is known to record rather loudly and may overload the audio.

Alex

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[Ronneil Camara]

Thank you so much Alex! I'll try this tomorrow. :)