Thank you all for your great suggestions. I think I’ve found the solution. Coincidentally @abcd567 , thanks to your post at Tweaks - #17 by abcd567 I ran the optimize-gain.py script, and with a small tweak (added some additional low-range gain values) I found something interesting- there were two ideal gain settings, one high (42) and one low (15), giving me a camel hump graph with two peaks, versus a normal bell distribution. Using the higher value, I can see aircraft with RSSI values around 29 or so. The lower setting lets me see aircraft with RSSI around 3 or so. It looks like I can’t see both sets of aircraft at the same time.
But back to the good news- setting the gain to 42 (it was 25 before), I can see a large amount of aircraft again! I’m only halfway through the day (and not even to the busy part) and I already have 4x the number of positions I did previously.
@glennblum That is an impressive screeshot. Which one of those antennas (if any) are you using? What gain value do you have set? Do you think heat shielding on the roof will offest the increased antenna gain when compared to the smaller outside antenna?
@chrislfa Yes, excellent points, and I (think I) have overcome those already. You described the situation accurately. I have a 6" USB cable from the Pi to a powered USB hub, and then have a 10m active USB cable plugged from the hub to the SDR on the roof. (30m is the max you can go with an active cable, requiring a power source like a hub).
And yes, my first power source was only 1.2A, I found out that issue the hard way already 
So my last two questions:
-
I still only get ~40msgs/sec … I was VERY surprised by @glennblum’s 250/sec metric there. Maybe that’s just because he has a bigger antenna? Or should I really be seeing more than 40/sec? Here’s my current map:
-
Is there anyway to catch both the small RSSI and large RSSI aircraft with one dongle? Or would I need a second dongle tuned to the lower gain value?
Thanks again to all - this has been a big help to me, and I hope my documenting my setup as much as possible here, it can help others as well. I am VERY open to additional suggestions in tuning the software, or trying new things.
Thanks!!!