Setting gain properly is at least important once you move the antenna outside.
I’ve done this for testing purposes today.
As expected the number of aircraft and the number of messages has been increased, mainly caused by an increase of range by approx 30 NM
But after i adjusted the gain to a lower value, also the number of Positions got an increase.
This is the graph where i mounted the antenna outside and later changed the gain.
The first vertical line is the moment antenna was moved outside. The second vertical line shows the change of gain to 40.2
The red box indicates the increase of the Positions/Second.
Messages > -3dB are still too highy, but i am continuing with experiments
Messages per second went up to 1250-1280 in peak times. Seem that the max. is achieved this stick can handle (as documented in a different thread)
I have my feeder placed at my local airport. Now that I’ve put the antennas on the edge of a roof overlooking the runway (from inside the attic) I’m losing the local traffic as it gets close. (while going from 1500 to 3500 aircraft per day and )
I’m using the orange USB prostick with the 978/1090 filter and the flightaware 978 antenna for UAT traffic and the blue prostick plus with the 1090 flightaware antenna for 1090. Local airport traffic (in the pattern) is the most important for me to capture and display.
Questions:
Is it possible to be to close regardless of gain settings?
How do you set the 978 gain?
What would be the best method to set the gain(s) based on my local traffic requirement?
How do you do the graphs for 978 vs 1090? (I’m just installing the 1090 one now to see if I can get it working)
Assuming you’re using a PiAware sdcard image, piaware-config uat-sdr-gain 20 (or whatever gain value)
then sudo service dump978-fa restart
The ideal way would be trial and error while you have a cooperative UAT-equipped aircraft hanging around on the ground. Tuning UAT gain is generally going to be difficult just because there is not much traffic on 978.
For UAT, i’d recommend adjusting the gain so that the weakest signal is at -30 in the signal level graph.
Then if you still lose local traffic, you can reduce gain further. Or you can increase gain again if that is not a concern and the range has suffered. But it’s a good starting point.
For 1090, uses the first graph and adjust the percentage of messages >-3dB to around 1 to 5 percent by adjusting the gain.
Further fine tuning will be done with trial and error, but that’s a good starting point based on the graphs.
(this is described more accurately here Thoughts on optimizing gain - #2 by wiedehopf , the percentage is the same as displayed int the graphs but only applies to the percentage since dump1090-fa was restarted)
I’m having a hard time optimizing for local traffic as different planes/equip have a large range of signal strength. Is it possible to set up multiple receivers on 1 pi with different gains and combine the data or would multiple pies be required and could that data be combined on one tar1090 display?
I’m using a pi 3. I really just want local traffic. Ideally from 500 feet from antennas to about 20 miles. Local display is all I really care about as I have it set up in the lobby of my airport FBO.
That should be doable with one dongle if you reduce gain sufficiently.
I’m not sure where exactly your receiver is, maybe you have some shadows that you think are too strong of a signal?
If the plane is behind a metal shed for example (no line of sight) and there is nothing appropriate that can reflect the signal you are going to lose reception even quite close to the receiver.
What gain are you running and what does your signal graph and message range graph look like?
Let’s try a gain of 20 and check how that goes.
I’m not sure how the LNA in the ProStick Plus handles strong signals, so that might be a problem.
In that case you would need some attenuation before the signal enters the ProStick.
Not sure how to best accomplish that.
Thanks. The data “gap” could be being masked by the roof. I get the planes on the ground taxiing where it looks like it could be blanked, however, I get a gap in the same area when they do a low approach over the runway which is why I thought signal strength. I guess picking up reflection off the taxiway somehow?
I’ll leave it at 20 for the time being and see how it looks tomorrow. Unfortunately I can’t access remotely as the internet is cellular and I can’t forward ports.
Will also look at relocating antenna to the front of the building if possible to eliminate any possible masking.
The coverage graph looks like it could have some obstruction reducing its view towards the North West and South East.
Basically any time the antenna doesn’t have direct line of sight to the aircraft, don’t expect to have reception.
That also applies to aircraft which are quite close.
The probability that you will receive a reflection from a metallic object is bigger though.
I doubt that asphalt will reflect 1090 MHz at all.
So if the roof is not flat, moving the antenna to the other side of the building might give you the reception you are looking for.
Nope. https://flightaware.com/adsb/stats/user/wgbiii#stats-108469 is the receiver in question. The other one does have a great view to the NW but has some trees to the SSE. (I’m playing with its settings as well as I was losing the skydive plane as it flew close by)
What’s strange is I was getting reception without line of sight to the taxiing aircraft and lost them when they took off right in front of the antenna.
It is a flat roof, however, I can’t see the antenna from all of the runway. I’ll try to move it next week.
I don’t remember. I’ll experiment more tomorrow when I go back out the the airport and keep notes this time. Hopefully, there will be more local traffic staying in the pattern so I can do real time checking. Seems like i was better off before upgrading the antenna!
That could well be the case.
As i wrote before if the LNA is being overloaded, the only thing you can do is put in an attenuator like the one i linked.
But 20 dB is quite a lot, so that might be too much
You could try a dongle without LNA, like the rtl-sdr v3.
