FlightAware Discussions

Troubleshooting 'Other' data

I have recently set up a receiver (I am new to all of this), and have noticed I am getting a huge number of ‘Other’ category positions (more than valid ADS-B and MLAT positions combined).

I check the page from time to time, and note that sometimes I am synchronised with over 300 other MLAT stations, and sometimes only a handful.

I’m not sure where to start troubleshooting, or whether it’s just a symptom of poor antenna placement. I can’t do a lot better with what I’ve got, which is indoors, but if it’s a configuration issue I’d like to try and get to the bottom of it.

I have checked that the location is set correctly. Please let me know if you have any ideas or need further information, any help is appreciated.

First I’d suggest installing collectd data logging using @wiedehopf’s script: https://github.com/wiedehopf/graphs1090

That will give you some data so you can compare the effect of what you change and it will give you a better insight than the FA stats alone. We need a bit more information before anyone can advise you on what to change. What is your current receiver setup? I’m assuming you are using an rtl dongle of some kind - what antenna/coax and any filtering or amp?

There’s all sorts of changes you can make depending on what you are doing at the moment which could help improve your results - if your only option is to have the antenna inside, then having it in a loft space will be better than in a room. If that’s not possible, try to have it in a window and away from other electronics (such as TVs and monitors, as they can be quite electrically noisy).

I would monitor it a while for some days.

I remember a friend of mine located in Tenerife had a power outage for almost a day which also brought his receiver down.
After he came back online, he also had a large number “other” which then went down to normal the next few days.

I had my antenna inside also for the first few months, at the end the values for “other” remain the same after i moved it outdoor.

Which type of stick are you using?

Can you try a different power supply?

Checking in to say thanks for the suggestions so far. I’ve installed graphs1090 and will keep an eye on it, and will try another power supply on the Pi as soon as I can get hold of one.

I’m using this primitive receiver and antenna, no filtering or amp: https://shop.jetvision.de/epages/64807909.sf/en_GB/?ObjectPath=/Shops/64807909/Products/53200

I have read elsewhere that trimming the antenna to 69mm (a quarter wavelength for 1090MHz plus 2mm) may improve performance, but don’t want to inadvertently break anything this early. I may try repositioning the antenna over the next couple of weeks when I have a bit more time.

If it’s a case of “this is likely to be the best one can get with this hardware indoors” then that’s fine by me, I’m glad it works at all for such a small project!

No you definitely have to trim it, the difference is huge.

How to improve performance of whip antenna of DVB-T

The can below it also helps greatly.
If you are afraid of cutting the whip, unscrew it and use a makeshift whip from copper or even steel wire.

Even though all shops say those whip antennas are for 1090 MHz, they actually for a whole other frequency: 800 MHz or so DVB-T.
They all want you to buy their more expensive antennas, so the cheap ones are bad on purpose. (or they can’t get cheap ones which are actually somewhat optimised for ADS-B)

Thank you. I’ve trimmed it and added the can…

Another alternative, if someone wants to retain the whip un-cut: un-screw whip and use a thin steel or copper wire, cut to proper length, as whip.

I started with the same setup, except that i am using the blue FA stick.
Then i replaced the original antenna tip with a wire in the correct length.

Gave me an improvement of 30% overall
The blue FA stick has a filter and an LNA included. Or you can use a seperate filter and LNA on your stick. Will give you additional performance as well.

Trimming the antenna seems to have resulted in decreased performance, especially with MLAT.

Or perhaps there are just fewer flights today!

You got a can below it?

Also antenna position is quite critical indoors.
The antenna should be above the electronics and upright obviously.
The electronics emit noise and if the antenna is above them it’s not picked up as strongly.

@wiedehopf

Fullfils all your conditions: :slightly_smiling_face:

  1. Close to window
  2. Above cookie can
  3. Whip cut to proper size
  4. Above electronics (above stereo deck)

.

Bonus:
Cookie_Monster

My site has been seeing a number of “other”
Aircraft. Several days ago I reduced the AirSpy RF gain 9 dB. Previously the system was “optimized” for max message rate. Now the gain is lowered to the point that few signals reach 0 dBFS. I tend to make one change and wait a few weeks or a month to see results. This last change is immediately visible in the “other” aircraft daily counts.


As the site’s daily count is around 5,000 a reduction from around 450 to 150 is significant.

Nov 25: I did a generation-hopping upgrade today. AirSpy code from v1.37 to v1.85. Gain reset to 21. Default options.

If you update to the most recent version of the airspy decoder, there is now some filtering which will largely eliminate spurious data, and allow you to put the gain back up to optimise message rate and range. Have a look on the airspy decoder thread if you haven’t seen it.

That’s definitely the case with Airspy. The software was polished a lot in the last couple of weeks.

Thanks. I’ll upgrade the Airspy code: I’m down several generations.
Nov 25: I did a generation-hopping upgrade today. AirSpy code from v1.37 to v1.85. Gain reset to 21. Default options.

I haven’t looked at the UK leaderboard for quite a while and I’m stunned to see that there’s a new top station with over 1,500 ‘other’ aircraft/day. Even being in the busiest location, I struggle to see how anyone can realistically see that number of ‘other’ aircraft.

Oh, and watch out @suffolk3000 and @caius because I’ve got you firmly in my sights now the aerial has gone up :smiley: :smiley:

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Ha, you will easily be on the top I think, and legitimately so - you have a nice clear horizon and flat terrain. :slightly_smiling_face:

That guy seems to not have updated his decoder with the current one (from the numbers I’m guessing he’s using an airspy), and is probably using the -x switch, which produces a lot of bogus data. Almost all of the “other” aircraft seen by him will be false. Have a look at the graph for me, suffolk3000 or andy b, and you can see really clearly where we started using the new decoder. A hit in the stats, but at least the data is real.

Until FA update their filtering there’s not much to be done about it.

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probably wrong thread?

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That is not as important as the location.

There are many sites here with flat terrain and open horizon that don’t pull not even close as much because… there are no planes flying around.
@keithma numbers are big close-by, the far-away ones help of course, but they are not the main reason for the positions - 67% of his positions are in <100 mile range, 95.5% are in the <150 mile range:

Also, it “helps” that his “Other positions” is unusual high. I won’t comment, I already said something about FA taking those in calculation…

LE: My “Other positions” numbers are very small with the -w 3 option.