FlightAware Discussions

Fluctuating Positions

Hello All,

My coworker got me into flight tracking, and I’ve been hooked ever since. So, I’m still new to all this, but I’ve learned a lot in a short amount of time through this forum.

I’m having an issue with the number of day-to-day positions. See the first screenshot below. I’ve also added some performance screenshots for more reference. The positions fluctuate a lot despite the fact that the number of aircraft reported stays relatively constant. My antenna is currently setup by the window and is located indoors since I don’t have access to the roof. I’ve listed my hardware below. I thought that adding the Uputronics on 8/1 would help the situation, but it only accentuated the problem. Any help would be greatly appreciated!

Setup:

  • Raspberry Pi 4
  • Uputronics 1090 Filter/Preamp
  • Piaware 5
  • Flightaware Pro Plus (blue dongle)
  • 1090 MHz ADS-B Antenna - 66 cm / 26 in
  • 25 ft Low-Loss Coaxial Extension Cable

Settings:

  • Gain = -29.7

Some questions:

  • I know that number of flights, time of day, and other factors play into the number of positions, but does it really fluctuate that much? I’ve compared my graphs to other sites within a 10 mile radius, and their numbers seem more stable.
  • I’ve set the gain down to -29.7. Should I lower the gain more? I lowered the gain briefly beyond -29.7, but that ended up increasing the messages > 3dbfs to roughly 20% maybe 30%.
  • When I looked at other people’s stats near my site, their positions/aircraft reported were relatively constant. My numbers fluctuate. For example, on 8/10 my positions/aircraft reported were roughly 169. The following day on 8/11, my numbers went down to roughly 132 despite having more aircraft reported than the previous day. Is the positions/aircraft reported a good metric to check the health of my system?
  • I ran a scan on the frequencies around me, and there was a cell tower which my antenna was picking up. I ran the scan again after adding the Uputronics, and it did a good job filtering out those frequencies. What else can I check?










The positions and aircraft on your stats page are the ones which are processed by Flightaware and can differ from your real reception as far as i understand. But i do not know exactly how that works.
As you have graphs1090 installed, does it show there a similar deviation over the time?

The only that question comes to my mind is why the ADS-B CPU utilization shows that graph. It should be more consistent not having these sharp ups and downs

There are no negative gain values available on the rtl-sdr.

Electronic devices near your antenna that are on and off?
Some interference the uputronics can’t handle either.
But hard to say.

Can you show a 2 week view of the message count (first graph in graphs1090).

Yes. I started my setup in late June of this year. After a couple of days, I started noticing the fluctuating numbers.

Here you go. Before 8/1, I didn’t change my gain. Only after adding the Uputronics, I changed my gain settings since the messages > 3dbfs increased significantly, but that was expected.

I don’t have any electronics near my antenna. Although, my raspberry pi along with the dongle are near my laptop. Not sure if that would cause any interference, but I might as well move the raspberry pi to verify.

I personally would also take a look on the device into the piaware logs for traces that not all packet reach the servers

Nah that’s not an issue usually.
I’d just ignore the fluctuating position on FA …

If graphs1090 looks reasonable then that’s just fine i think.

Most probable reason, if there are aircraft on ground sitting at Burbank and you receive those, you get lots of positions off that?

The FA position counting is a bit complicated and depending on what the aircraft are doing is wildly different.
I believe a position from aircraft on ground is sent more often.
With changing activity or maybe you only on some days when the weather is right receiving ground positions …

In general i believe you can get this all more stable if the antenna was on the roof?
Or is it already?
Anyhow i don’t see any technical issues.

I suppose you can check the piaware log

sudo journalctl -e piaware -n20000

you can scroll through that upwards see if anything stands out …

If it really is interference add an FA filter in front of the uputronics, compared to the uputronics it’s relatively cheap. (that’s a long shot but maybe worth a try if you want to throw some more money at it)

I’m struggling to see what’s wrong with that graph.

I looked at specific times in the logs where I thought there would be a noticeable drop and didn’t find anything. All of the packets look like they are getting sent. Here is an excerpt:

Aug 10 13:50:37 raspberrypi piaware[16590]: 297692 msgs recv’d from dump1090-fa (2125 in last 5m); 297692 msgs sent to FlightAw
Aug 10 13:45:37 raspberrypi piaware[16590]: 295567 msgs recv’d from dump1090-fa (2373 in last 5m); 295567 msgs sent to FlightAw
Aug 10 13:40:37 raspberrypi piaware[16590]: 293194 msgs recv’d from dump1090-fa (2263 in last 5m); 293194 msgs sent to FlightAw

The only thing that stands out in the logs are the messages below. I see them in other days as well:

Aug 12 08:35:37 raspberrypi piaware[16590]: 726783 msgs recv’d from dump1090-fa (1299 in last 5m); 726783 msgs sent to FlightAw
Aug 12 08:32:11 raspberrypi piaware[16590]: faup1090(16620): handleFaupCommand(): Adjusting message rate to FlightAware by 3.00
Aug 12 08:32:11 raspberrypi piaware[16590]: adept server faup request received: faup_adjust_upload_rate
Aug 12 08:32:05 raspberrypi piaware[16590]: faup1090(16620): handleFaupCommand(): Adjusting message rate to FlightAware by 1.00
Aug 12 08:32:05 raspberrypi piaware[16590]: adept server faup request received: faup_adjust_upload_rate
Aug 12 08:30:38 raspberrypi piaware[16590]: faup1090(16620): handleFaupCommand(): Adjusting message rate to FlightAware by 3.00
Aug 12 08:30:38 raspberrypi piaware[16590]: adept server faup request received: faup_adjust_upload_rate
Aug 12 08:30:37 raspberrypi piaware[16590]: 725484 msgs recv’d from dump1090-fa (1580 in last 5m); 725484 msgs sent to FlightAw
Aug 12 08:30:31 raspberrypi piaware[16590]: faup1090(16620): handleFaupCommand(): Adjusting message rate to FlightAware by 1.00
Aug 12 08:30:31 raspberrypi piaware[16590]: adept server faup request received: faup_adjust_upload_rate
Aug 12 08:30:04 raspberrypi piaware[16590]: faup1090(16620): handleFaupCommand(): Adjusting message rate to FlightAware by 3.00
Aug 12 08:30:04 raspberrypi piaware[16590]: adept server faup request received: faup_adjust_upload_rate
Aug 12 08:29:58 raspberrypi piaware[16590]: faup1090(16620): handleFaupCommand(): Adjusting message rate to FlightAware by 1.00
Aug 12 08:29:58 raspberrypi piaware[16590]: adept server faup request received: faup_adjust_upload_rate
Aug 12 08:25:37 raspberrypi piaware[16590]: 723904 msgs recv’d from dump1090-fa (1582 in last 5m); 723904 msgs sent to FlightAw

It’s an indoor setup. I definitely agree that these issues could clear up if my antenna was outdoors.

You and me both. It’s the positions that fluctuate that have me scratching my head.

Just checked my logs, i cannot find any entries like these. Maybe that’s an issue?

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Yeah that’s not normal.
Probably an unstable internet or wifi connection.
Edit: Above is wrong, it’s completely normal when Skyaware Anywhere is being used.

@obj when does piaware do that, can you confirm?

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When SkyAware Anywhere is in use for that receiver - it increases the report rate to avoid slow updates of aircraft where usually we wouldn’t report them frequently.

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“Positions” on the site stats page is somewhat misleading. It’s really “data reports made to FlightAware”. The report rate depends on a lot of things that are out of your control - notably what the aircraft is doing (e.g. flying in a straight line at FL390 is not worth reporting frequently). If you’re also using skyaware anywhere (your logs imply you are) then the report rate gets artificially increased while it’s in use to improve the interactive experience there, which unfortunately also shows up on the stats page.

I’d rely more on your locally gathered statistics as they are unaffected by the reporting rate decisions that piaware makes.

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Just so I’m clear, when the rates increase, I am assuming that the number of positions also increase. Is that correct?

I usually leave SkyAware Anywhere running on my Pi receiver. It sounds like this is not recommended. Can I use a different computer on my network and leave Skyaware Anywhere running on that machine or will that also artificially increase the report rate?

Why wouldn’t you just use the local interface?

http://127.0.0.1/skyaware
That from the receiver i believe?

Otherwise … network IP from the network.

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To be honest, I thought it was the same thing. It is definitely not.

In any event, I’ll leave my Pi receiver alone and post here if there is a change in the behavior of the positions. If not, I’ll try a reinstall of the OS and Piaware.

Thanks everyone for all your responses! Very helpful!

There is no need to reinstall, the numbers on the FA stats just fluctuate when skyaware anywhere is used at all.
That’s just how it’s designed and i’m sure it’ll be reason for discussion again …