FlightAware Discussions

How do you test the health of your SDR?

I think I have a SDR that isn’t picking up as many aircraft as it should be. I swapped antennas and no change. Other than swapping SDRs, is there any command I can run to give me an idea of the health of the SDR itself?

If it’s still working and just not great, there is no test for that.

Using the official RPi power supply often helps, power problems are the number one problem with all kinds of charming symptoms.

Using 2 dongles on one RPi makes power problems even more likely.

To test it with a single dongle, can I just halt dump978-fa or do I need to disconnect the USB cable from the 2nd dongle?

It will still be drawing power, so unplugging it is a good idea.

Also it can’t really exclude a bad power supply, the voltage could still be low even with one dongle.
That would just mean the power supply went bad or semi-bad.
It happens with some supplies, they are often made to charge phones and not run all the time.

If you like running two dongles, get yourself the Official RPi power supply, it’s about 12$.

I’ve got an RPi supply but I’m also using a 12-foot extension. Made the mistake of buying one without checking the AWG - turned out to be 22 AWG which caused a 1V drop at the RPi board (~4.1V). I’m now using an 18 AWG extension and the RPi voltage is ~4.8V.

I also have a 6V / 3A adapter I can use with the extension cable to get the RPi voltage closer to the upper limit of 5.25V. Haven’t tried the 6V adapter yet.

Is it purely an adapter issue or are there defective RPi 3B boards out there? I’m not using the B+ . IF there are some bad boards, I can try swapping it out for a different 3B.

Put the supply in the box and don’t use an extension on the low voltage side?

The RPi boards have power protection which drops the voltage by around 0.1V.
Plus cable/socket losses.

Dongles want 5.0 V for best performance, that’s just a fact.

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Not an option. I’ll give the 6V adapter + extension a try tonight.

That’s dangerous.
If anything you’ll need an adjustable power supply to stay in a somewhat safe range.
Your voltage drop at the moment is around 0.3-0.4V.
If you use the 6V supply you will overvolt the system even under load as the voltage will be around 5.6 V.
And in case there isn’t any load when the system starts up or reboots, then it might even spike up higher.

I’d recommend a DC-DC converter if you don’t want mains voltage in the box.
(24V to 5V or 12V to 5V)

Otherwise the voltage will fluctuate too much.

I suppose you could go with 14 or 15 AWG and get away with an adjustable power supply at 5.3 V.
Or maybe the current cable would also be fine with 5.3 V, hard to say.

But i really wouldn’t go any higher than 5.3 V on the input to the cable.
As soon as the load drops for some reason the higher voltage could potentially give you a dead board.

I’ve thought about that but was worried about reliability in a hot, enclosed outdoor box. Do you have any recommendations for a 12V-to-5V DC-DC converter?

An electrostatic discharge, perhaps? I had one Pro+ dongle that was not working right. I remember touching the antenna, and hearing the ‘click’, before I noticed something was wrong.

It would not receive a lot of planes after that, and the clocking alert was on more often than not.

Maybe check in this rather recent thread:
DC-DC converters (for running your Pi)

Just get one one ebay that states an output of 5A, then you should be good at typical required voltages.
Adjustable output voltage is of course a plus.

Maybe you can ask @keithma for an ebay link :slight_smile:

I use these ones - Rated at three amps (if you add heatsinks).

Without a doubt, the best (only?) way to check an RTL dongle is to compare it to another (preferably side by side).

could maybe try using rtl_power and see how well you can see GSM frequencies much easier to see that ADSB.

How do you compare to others in your neighborhood? If you are about equal than try in line filtering. I drastically increased by counts/positions with a cheap SAW filter.


Bob, which antenna are you using?

Haven’t seen any on ebay for less than 15$

For 30$ you can get an rtl-sdr LNA with 2 builitin SAW filters.

Some of those noelec dongles even have builtin bias-t, don’t they?
Otherwise external bias tees aren’t too expensive either.

I just checked my percentage of strong messages and it was 10% - hmmm, maybe I’ll dial back the gain some.

%strong command =

awk "$(cat /run/dump1090*/stats.json| grep total | sed 's/.*accepted":\[\([0-9]*\).*strong_signals":\([0-9]*\).*/BEGIN {printf "\\nPercentage of strong messages: %.3f \\n" , \2 * 100 \/ \1}/')"


Gain of 30 or 40 was too low - less than 1% strong signals. Tried max again and strong signals are now ~5% so I’ll leave it at max (using DIY 1/4 ground plane antenna with 12" cable to SDR).

available gain settings:
0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4
28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6

You never change gain by 10 if you are anywhere in the correct ballpark already, which you are.
Try 48 for example or 49.6 if you were using -10 before.

So, I tried the FA blue filter on my FA plus SDR (with built in filter and LNA) and it helped. Next I tried a Mini-Circuits vbfv which I think is a SAW filter (for $9 US why not) and it worked maybe a little better than the FA blue filter. I’m in a high RF environment with two TV stations, two AM stations, and a cell tower all within a few miles. Am using a FA stick antenna with lmr 400 cable. Have most of the PI and SDR stick in an ammo can. All in an effort to keep RF from sneaking in,


Mini-circuits filter