I misunderstood the Thoughts on optimizing gain threads then. I understood them to indicate that reducing “strong_messages” would increase messages for close AC.
I ran the command found in those threads and was at Percentage of strong messages: 16.473 and after changing gain from “max” to “49.6” (the next step down?) I am at Percentage of strong messages: 1.320
That was my reference to significant change in the positive direction
I am using a Pi3B+, FA ProStick Plus (the blue one) and the FA 1090Mhz (green) antenna.
Edit: (including a couple 8h graphs with the gain change approximately in the middle)
I think the idea is that close aircraft are already strong messages, and with your gain set to max they are amplified further, drowning out all messages, both near and far. The optimizing gain thread is really about the balance between having enough gain to pick up the more distant aircraft without the nearby ones killing your reception.
There’s no one right answer that serves everyone. Some may not have a ton of super close aircraft and want to crank up the gain to try to get more distance. Others my have so much local traffic that they have to sacrifice distance in order to get anything at all. It’s a balance that is unique to every situation. That 5% strong messages recommendation is a guideline for a starting point.
No that’s not correct.
ADS-B/ModeS happens in short bursts so even setting the gain quite high you usually don’t get overload for the weaker signals.
I just meant the graphs don’t show a direct uplift in the numbers.
Anyhow the lowered gain should give you a better margin for close by aircraft.
It’s not nice if a helicopter flies by and he’s either obstructed or so close that he overloads your receiver
Sorry, I’m confused. You are saying that while that nearby helicopter is “overloading your receiver”, the receiver is still picking up weaker signals? I don’t understand how that works.
ADS-B messages are very short bursts, 50-100us long. Receivers can recover from overload relatively quickly, so a close/strong ADS-B message that deafens the receiver doesn’t prevent receiving a weaker message from a different aircraft a bit later.
The track of the aircraft UMV is disrupted due to overload on final approach close to my receiver (dashed line as it crosses the coast), but the track for the other aircraft is not disrupted over the same time period (MMV -both Cessna 208 tandem sky diving aircraft if anyone is interested).
This is for an Airspy Mini with the gain set at 20 (max is 21), as I’m more interested in receiving distant aircraft and can accept brief overload by very close aircraft as a trade-off.
The other thing that the plot demonstrates is that overload is fairly sensitive to altitude, as well as distance. UMV didn’t overload the receiver on ascent when it passed within 1.25NM at approx 3800 feet above the receiver, but the overload commences at 1.75NM distance at approx 1700ft on descent. The angles from the receiver to the aircraft are 27 degrees and 8 degrees respectively. This is what is expected given the receiver and transmitter antennae are oriented to optimise signals sent/received in the horizontal plane.
