FlightAware Discussions

Mlat drops out. Only reboot makes it come back

Hi everyone,
Was using a pi zero, rtl-sdr.com V3 dongle for serving flight aware. Raspbian stretch.
Mlat kept dropping out (even though I am regularly synchronised with 600+ other receivers)
Thought it was CPU overload so moved set up to RPi 3B. Raspbian buster, CPU load way lower. CPU temp never over 42 degrees Celsius.
Mlat still randomly drops out.

USB issue? Can I do anything about it other than restarting, stopping dump 1090, switching on bias tee from command line, restarting dump 1090?

I have some shell scripting experience, so is it possible to write a script that detects the non synching in the logs and then does the restart process as described?

Thanks for reading. Suggestions welcome.

Make sure you have the latest kernel, there was a problem with buster and rtl-sdr devices:

sudo apt update
sudo apt dist-upgrade

Apart from that the power supply is the most likely problem.
Also make sure you have the location set precisely (at least 4 decimal digits).

You can script automatic reboots when the clock is unstable, but i’d check for the other possibilities first.
If you want some inspiration in regards to scripting:
Dump1090-fa stops sending messages after some time

It checks for the stick giving up completely though as you can see with the grep command.

Ah yes the kernel.
Will check of that list of yours and report back.

OK - already on latest kernel. dist-upgrade didn’t do anything at all.

Power supply check next. I know I’ve got two official power supplies (one new one for my pi4 :slight_smile: ) but couldn’t swear about the third.

My co-ordinates are recorded to 5 decimal places, so I suspect that’s good enough.

On the pi-zero I think I put an entry into crontab that rebooted every 15 minutes, I think - it was a while ago - because the dongle was shutting down. Hmm - seeing a pattern…

Ah that’s interesting.
In the logs, the faup1090 command line is supplying only 3 decimal places for my position.

That’s normal and irrelevant to the problem.
Also 3 decimal places are good enough, though 4 are better.

Are you using an USB extension by chance?

Might also be that the dongle is just toast.

Yes I’m using a lead from the pi to the dongle.
Maybe that’s toast. I can swap that out and see.

Just don’t do that if possible. It reduces the voltage that goes to the dongle, which causes performance to degrade.

But if you have a good power supply with enough voltage and an USB extension with sufficient copper in it (hard to tell), then it should still work.

Seems sensible. I think it’s a cheap cable and I have just bought a couple of significantly better ones which have a LOT more copper, one of which is only supplying power to a fan.

Time to have a swap around and see what works best.
Thanks for the suggestions.

The dongle is also supplying to the uputronics lna, which although isn’t a huge current draw might be a factor I suppose (especially if the USB extension lead is dodgy)

OK. Mlat hasn’t dropped out at all since I connected dongle directly to RPi.

Interestingly, the plane and message count has dropped by 30% or so.

Did you have to extend your antenna cable?

When I raised my antenna I added a 25 foot extension with a union and lost nearly 50% of my tracking numbers.When I lowered the antenna just enough to remove the extension the numbers came back up.

One other thing, when I first set up my system I let it choose it’s location. I would drop Mlat a lot. So I loaded an app on my phone and used it to get current location and then measured the height above ground. I then plugged those numbers into the configuration and Mlat works a lot better.