FlightAware Discussions

Aircraft Trails

Can someone explain on a technical level what is going on with the two aircraft with dash marks in their trails? I would imagine that indicates a lack of reception at that point in each aircraft’s position, but more detail about what is occurring would be appreciated.

GitHub - wiedehopf/tar1090: Provides an improved webinterface for use with ADS-B decoders readsb / dump1090-fa

Terrain obstruction.

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The line is dashed when it’s connecting position reports that are > N seconds apart. (the exact value will depend on exactly what software you’re running).

Terrain obstruction (as wiedehopf says) or the transponder antenna being temporarily obscured (e,.g. during turns) are probably the main two causes.

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Not certain of the reason, but I’m seeing many more dashes than I used to. In fact, nearly every aircraft trail now has a dash in it somewhere. Perhaps removing the filter before the pre-amp wasn’t such a good time after all.

Show a screenshot of /?pTracks if you’re using tar1090 already as described here:
GitHub - wiedehopf/tar1090: Provides an improved webinterface for use with ADS-B decoders readsb / dump1090-fa

And consider adding the outline (GitHub - wiedehopf/tar1090: Provides an improved webinterface for use with ADS-B decoders readsb / dump1090-fa)

That will give you a much better picture of what is going on.

Doing pTracks screenshots with and without the filter … is likely to answer that question.

You have the tools already … just have to use them.

If the dashed lines are over your location, if can mean the receiver is overloaded. Try reducing the gain.

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@wiedehopf The 12 hour tracks are no longer showing the dashed lines. I reduced the gain from 32 to 26 on Wednesday at approx. 18:00 and the graphs below clearly show that change take place.



Although I’m no longer seeing the dashed lines, to my eye the overall performance has decreased. Aircraft seen/tracked appears to have increased, but apparently at the expense of some range.

I also do no know which signal strength profile is preferable. After the gain reduction of before. (although I see noise went down which is good)

/?pTracks doesn’t have dashed lines.
But you can clearly see a couple of directions with more range than other directions.

Overall seems to be quite constrained by obstructions but without they heywhatsthat info and knowing about close in obstacles … can’t say.
GitHub - wiedehopf/tar1090: Provides an improved webinterface for use with ADS-B decoders readsb / dump1090-fa

Obstructions are certainly an issue as my only option for mounting the antenna is near a first floor window. However, that has always been the case. Nothing new about it.

Several days ago I removed the FA filter that had been in front of the pre-amp, which initially showed an increase in performance. Then shortly thereafter I began seeing lots of dashed lines. In fact, almost every trail on my receiver has dashed lines now.

Definitely a mystery because there are no new obstructions or obstacles at play. The only thing that changed was removal of the filter.

Well either you have intermittent interference from some device in the kitchen or something … or ham gear?
Put the filter back then.

Worst case would be a solder crack in the uputronics (that happens with the connectors) that would result in an intermittent signal.

The dashed lines didn’t appear right away, so I don’t think the lack of filter is the issue. Nothing new in the area either as far as sources of interference.

I really hope the Uputronics isn’t the issue. I read about potential weakness regarding the jacks so I’ve always been careful with it.

You have the 2 week signal / range and message rate graphs (first graphs) and can say when you removed the filter?



The filter was removed on Saturday the 9th. I lowered the gain from 32 to 28 on Wednesday the 13th. The dashed lines began to appear around Tuesday the 12th.

Saturday is generally pretty light in terms of traffic, but you can see there that the dashed lines appear at very close range as well as further out.

Only thing i can think of is that you changed something near the antenna that obstructs it further. Or maybe the weather changed, humidity or snow could add to the existing obstructions i think.

Filter indeed doesn’t seem to be necessary.
Due to the obstructions some signals are very strong while a lot of them are very weak.
So i guess that means … removing the filter reduced the attenuation so you need to reduce the gain to prevent overload?
Yeah i suppose that could be it.

Then you could have changed tar1090 (disabled P or something) … or i changed the code for the dashed lines without realizing (happened before … not that i’m aware i changed it recently).

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I don’t think tar1090 is the issue because SkyAware shows the same gaps in the trails.

Not really sure what new interference might have popped up in my area. Nothing has changed that I’m aware of, but there could be factors at play beyond my knowledge.

One quick question about the range graph. In the min/max data below the graph, my max range is never displayed. The numerical value is always replaced with a strange symbol. Is this a known issue or something with my system?

There is not to be supposed a number there.
Hmm … not sure why there is max and peak range …
Anyhow the number for peak range is what you want i guess.

The average max range is the average of all the peak ranges in the period. The peak range is the highest value seen during the period.

Yeah it doesn’t make sense to have the blue square next to both though :slight_smile:
Oh it does it’s the line at the top.
But it should probably have another color :slight_smile:
Oh and the avg. max range is a line as well.
So it does make sense … i just didn’t remember what my logic was when i programmed it … happens.

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