FlightAware Discussions

Not seeing ADS-B equipped low and close to Antenna

Suggestions? Settings?

We are not seeing ADS-B equipped aircraft on our two antenna system (978 and 1090) until they are more than a few miles away from our gliderport, Soaring Club of Houston. I know for certain that the aircraft are transmitting properly. I can see the aircraft on my iPhone (almost live) via the FlightAware app, down to 200 feet AGL. All the aircraft have clean PAPR’s (Public ADS-B Performance Reports). I cannot see the above aircraft (four total - all 1090) on the local computer hooked up to the two orange FlightAware boxes. This has been the case from the beginning until now, about four months. At first, I assumed that the problem existed in our local aircraft ADS-B systems. Now, I’m pretty darn sure that the problem is not on the airplane. I’m guessing that the problem is on the user end, me.

Yet, we can see almost hundreds of other aircraft up to 100+ miles away.

Is there setting that I need to change?

Today, I watched a 1090 equipped airplane start its taxi (transponder ON) that was parked 50 feet from the antennas, takeoff and then fly towards the NW. The airplane didn’t appear on our local viewer until it was about 8 miles away. Yet, I could view the airplane almost live on my FlightAware app on my phone.

Site 105801 (1090 ES)
and
Site 107621 (978 UAT)

Thanks,
Jamie

Possible reason could be too much noise which prevents the receiver from getting the proper signal.

Is it a Raspberry? Did you try reducing gain?
We might need more details about your setup. Which devices you’re using, which antenna etc.

There’s also a blind spot for aircraft which are right above your antenna. These cannot be seen for a short moment.

This is likely to be just a gain setting that needs tweaking; there is a “donut effect” around a receiver where close signals can overload the receiver (the hole in the donut). Usually we’ll tweak that for on-airport FlightFeeders after install (because they are much closer to aircraft versus your average receiver) but it may have been missed in this case. Let me get back to you.

It is a FlightAware FlightFeeder. How is the gain adjusted?

Attached pic: one antenna is for 1090 ES and the other is for 978 UAT. I don’t know the specs but they were supplied by FlightAware.

Thanks,
Jamie

We can adjust the gain remotely.

Great. Can you post after you have adjusted the gain so I can check?

Thanks,
Jamie

The gain is adjusted on your 1090 feeder. Can you check if close range signals have improved?

You can also adjust and experiment with the gain through the FlightFeeder GUI. Navigate to System -> Radio -> Radio Gain

eric1tran
It seems that there was no improvement with the remotely adjusted gain. When I viewed the gain settings on the FlightFeeder, it was not obvious that the gain was adjusted - it said “max gain”. I adjusted the gain down to 8 and was able to see the local aircraft less than 0.5 mile away as they departed our gliderport. I didn’t have time to experiment at length with different gain settings. I’d like some guidance as to what you would expect with 0 (zero) gain selected versus 8 (as currently set) versus “max gain”. Below are two screen shots. The first one has “max gain” selected and the second has 8 selected for the gain. The lower gain clearly shows less traffic at greater distances.


This is the tradeoff. Lower gain will help with close aircraft at the expense of range.

For installs like yours, we’re usually more interested in the nearby/low aircraft, because there’s already good coverage of high/distant aircraft from other receivers (high aircraft can be seen at long ranges)

Thanks. What would you expect if I set the gain to zero? It is currently set to 8.

Thanks,

Jamie

I don’t think we ever set the gain that low; even 8 is pretty low. The range is approx 0 - 50 (and it is a logarithmic scale).

Ideally you want to set it as high as you can without losing close aircraft.

setting it too low can also an issue identifying planes.

Be aware that the signal are not at the same strength for aircraft in same distance.

I would start with a higher gain and reduce it step by step.