FlightAware Discussions

Noise Level Display with dump1090-fa

Is there an easy way to display in realtime dump1090’s measured noise level?

You could monitor the stats json which refreshes once a minute or so.

What is the problem you’re trying to solve?

In Stratux Europe we switched to dump1090-fa and might look into some advanced gain adjustment based on noise level similar to how we currently do in th OGN receiver path.

Yeah, the json stats is probably a good start for that. See https://github.com/flightaware/dump1090/blob/master/README-json.md#statsjson for a starting point (it is a little out of date - it’s actually missing the noise field, but the field is present in the actual output).

The json files are by default written to /run/dump1090-fa/ once a minute.

Thanks, this is a good start. I am already collecting some data on the ground but this certainly needs to be done also during flight.

Be aware that in Europe that noise number will significantly increase with aircraft count / message rate.
Partial messages that can’t be decoded count as background noise as such this fluctuates quite a bit even with a steady setup.

I’ve found it more useful to just create a statistic over the dBFS for all aircraft in the aircraft.json.
The minimum for that is often a good indication for the noise level and it doesn’t fluctuate with traffic as much.

But i’ll need to re-add the noise graph to my graphs1090 scripts …
Didn’t want to make it even more complicated so i switched to have a “noise level” for all receivers, not just rtl-sdr.
But better to have the extra graph.

Sure, this would be helpful. For your background: the current Stratux (both US and Europe version) defaults to max. gain (I assume 50dB) so it might make sense to investigate a bit more and collect some data during flight.

Isn’t the stratux for pilots on planes or something?

Even without an LNA that sounds like too much gain and overloading the receiver.
Also do you even care about traffic further than say 50 nmi?

Oh you’re already using the graphs?
There are other factors to determine a good gain setting:
Thoughts on optimizing gain

Yes, Stratux is a very popular DIY traffic awareness device:

It combines a dump1090 instance for ADSB and and OGN decoder for traffic in the 868MHz frequency band.

As pilots we indeed do not care about traffic further than 50 NM unless it is a rocket …

not yet but I would love to integrate it for testing - maybe I should wait until youre-add the noise graph

I’m surprised you’re using that much gain then.
Unless you have a really crappy antenna + placement i suppose.

Nah it’ll be useful either way i’m pretty sure.

This gain setting was grandfathered from the Stratux US version, no one ever looked into this.
This is how a classic Stratux looks like, 6db antenna gain but quite some RPI noise:

I modified my Stratux substantially, all metall case, shielded SDRs, passive cooling, here are some of my prototypes:

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That’s very likely much lower gain antenna.
Honestly i’ve never seen a rubber ducky properly tuned for 1090 MHz.

Those look nice.

Well that’s all the more reason to not use as much gain.

Though the default settings are AGC, if you have enough interference that might even trigger the AGC to actually reduce gain.
With the intermittent ADS-B signals it usually just sits at maximum (estimate gain of 55 to 58), while the manual gain settings available range from 0 to 49.6


Thanks… My screen is now wearing a mouthful of beer.