I have noticed lately after the latest rebuild, it seems like there might be a GAIN issue (FA Image). I use to have no issue, but now I have noticed when a craft is on a direct track to me (<1mile) it goes dark. Around -1.7 db I can hear them, but I will notice they sometimes go to -1.6, then "Last Seen" triggers off of NOW to a delay. Sometimes depending on the speed of the craft, it can be almost a mile before I hear him again (which is not a distance thing, it is when the RSSI climbs, I know its negative, and how RSSI works, so using layman's terms). When the RSSI goes back to >1.7 the craft pops back up. Now years ago I read about adjusting the gain, and 1.7 - 2 was about the strongest you wanted. Had no idea that transmission could be so "loud" that it would just garble it and make it go away. I have not had any issue until the latest FA image I used. Anyone have any suggestions? Do I adjust the gain in the config file on the root of the SD?
I really don't know ... but FA image probably set to auto-gain ... On the ADSBx custom image you can tell dump1090 to use auto-gain or some other gain value. if you look at piaware-config.txt on the /boot partition .. there should be a config for gain ... Or the new dump1090 FA released has issues. Or maybe your antenna has issues. Or maybe the SDR is having issues. Sometimes if you get one very close it will over power the antenna and SDR, when you have a good setup. We see that here under PHX when we get one low on final.
I am dead certain its not the hardware. Nothing has changed but the image. I'll check auto gain...I was thinking someone might have encountered this.
Sorry edited my post a bit after rereading it .. You likely have a good antenna and setup, but when something comes direct overhead it overpowers it. https://discussions.flightaware.com/t/need-to-adjust-the-gain/20213 Amplifing signals is always a trade off - do we hear the far away ones and risk too much gain on the close by ones ..
FlightAware Antenna, FlightAware SDR with built in filter, 24" antenna cable. What is strange it just started after the image change. Thanks for the link, I'll go read the gain info. Thanks for the response! Hope you had a good turkey day and are recovering.
Maybe you have something on a gain optimization script, see: https://forum.flightradar24.com/threads/11249-Gain-Optimization-Script Thanks to abcd567; I have used it successfully!
This might simply be a case of radio theory. Both the transmitting and receiving antennae are vertically polarised. This means that they transmit/receive most energy in the horizontal direction but very little vertically. This causes an effect which is called the cone of silence, and it used to be commonly employed to locate SAR beacons etc. When the aircraft is almost directly overhead the receiving antenna there will be the absolute minimum of energy transferred from the transmitter to the receiver. Although the aircraft is pushing out plenty of power - witnessed by the strong signal strength as it approaches your location - the amount of energy when the aircraft is almost directly overhead will drop significantly and, theoretically at least, should actually fall to zero. Once the aircraft has passed directly overhead and reaches the distance you mentioned (~ 1 mile or so) the energy transfer picks up again and you can receive the aircraft transmissions. In the worst cases, no amount of gain adjustment on your receiver will correct this, but the phenomenon should only be noticed on aircraft passing directly overhead so should only affect a very small number of aircraft for a very short period of time.
