FlightAware Discussions

Single tracks with bad decodes

Hi all,

I am trying to understand if there is a problem with my setup or if this is somewhat normal. Looking at the Perf logs, I see a lot of bad decodes according to the chart. I am using the latest version of piaware and 20% bad messages seems high. I have played with the gain a bit, but nothing really changes the proportion of bad vs good messages if I am reading this right. My antenna is in the attic but even before that when it was on the roof, it seemed to exhibit the same behavior.


I am using an RPi 3 Model B, Blue dongle, FA Antenna connected LMR400 cable (40ft). I recently did a clean install PiAware 5. RPi is connected via ethernet.


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Do you have lots of obstacles and many far away flights?

There are some big trees to the south of me and I am lot closer to Portland International Airport in Oregon. Also, my attic is all wood composition so no metal. About a month ago I move the antenna from in the garage to the attic. It increased the tracking results but the single track bad decodes still hung in there around 20%.

And not sure if this helps but shows a change of events resulting from my move:

The topic regarding the single tracks has been discussed several times, but i do not find the conclusion thread.

maybe @wiedehopf or @caius can help here
I can remember that my blue FA stick showed some similar charts.
Maybe you need an additional filter, but the experts need to reply to that

Looking at the % of >3dBFS (20.9), I would reduce the gain, first of all. Which one do you have currently?

I have been trying out that autogain script I found in one of the forum messages. Letting it run and to determine best gain. It seems to be best at 48, previously it was just on -10 (highest possible). I could try going lower to see if it helps. I do have the FA filter installed inline with the antenna using the blue dongle.

I am about 20 miles north of PDX in Battle Ground, WA. I have almost exactly the same setup as you, except that my antenna is installed on my roof, about 30 feet above ground level. It seems that your graphs aren’t too different from mine, but I would definitely be looking at reducing that gain.

I catch most of what comes out of PDX and VUO, and some of TTD, but due to the terrain north of the river, I can’t see anything below 750 feet or so.

20% strong messages seems pretty high to me. Mine hovers around 3.5% to maybe 6% depending on traffic, and I have been averaging >900 aircraft/day for the last 2 weeks or so.

You are welcome to use my stats for comparison if you are close enough to my area to largely be seeing the same planes. jafrank ADS-B Feeder Statistics - FlightAware

Thank you for that. Good to know and compare. I have been running the autogain script for the last hour. I think I am getting better results with it being busier closer to me than when I did it last night. It’s dropped the gain down to 40.2 and seeing the bad message level drop significantly. Sounds like gain is the ticket like everyone has mentioned. I will keep working with it. Thank you.

Gain at -10 for ADSB means “maximum possible gain”, not “automatic” as often stated. Good to see things are getting better.

Correct. Should have used better wording. I will fix. Thank you.

I was never happy with that script and tried different settings over several days.
The number of messages > -3dBFS should be below 5% in average.

As you moved the antenna to a better position, i would start the try and run with something like 42.1 or 43.4

For the blue FA stick with filter your setting might be still a bit high.

Just closing the loop on this topic. I settled in with a gain adjustment of 40.2 which is yielding me ~2.3% bad messages in the last 48 hours. So big difference overall. Here is what the last 7 days has looked like:

Now the last 48 hours:

We’ll see how this goes for a while. Thanks for all the input :slight_smile: