With my Pro Stick Plus, Uputronics filtered preamp and FA antenna I’ve been testing a few different gains and got the best results so far with it set to maximum manual gain 49.6 despite what appears to be a lot of in-band noise on the heatmap.
It performed way better than 20.7 which visually looks like the best signal to noise, so clearly interpreting these scans requires some appreciation of how well the receiver is able to cut through what looks like noise. It also performed better than 38.6 which looked to have more noise. It also performed better than 48 despite this seeming to be one of the noisiest levels.
With that appreciation in mind a gain of 49.6 also outperformed AGC and so I was curious as to what that actually looks like on the heatmap. So I ran the rtl_power command with gain set to -10 which I believe sets the tuner gain to an even higher value around 53.
Scan at maximum manual gain 49.6
Scan at Automatic Gain Control -10
It’s any wonder that AGC performs worse than 49.6; it introduces loads more in-band noise. Despite this, adding the preamp on AGC still outperformed the non-preamp setup on AGC.
Conclusion
It looks like AGC is good for Pro Stick Plus + FA antenna setups as long as there is no nearby strong interference, in which case a manual gain at or near maximum may offer an edge and a filter will help further.
For the filtered amplified setup it looks like AGC can be too much and doesn’t turn the gain down to a better value as its name implies. However in setting a manual gain it’s clear that the receiver does a great job of extracting signals despite what looks like noise on the heatmap, and so it’s best not to turn down the gain too much, and in my case having at 49.6 is giving the best result.
In otherwords, when using the results of gainmap to try and find an optimum gain visually, what looks like smooth in-band preamp noise drowing out the signal is in fact quite well tolerated by the receiver so don’t needlessly drop the gain too low as you’ll throw away signal that the receiver can actually use.
I will continue to test and see how stats pan out over the next week.
I’ve edited the gainmap script in the original post to add auto gain (-10) to the start of the testing.