Planes but not feeding

It changes the sample rate used for decoding: 12 MSPS or 20 MSPS. The latter gives a better performance on capable computers.

I use 12 MSPS decoding on a RPi3 to save some power because the system is running on solar power. This also saves some USB bandwidth which results in better MLAT (less packet drops). The RPi is not what I would call a power horse…

sudo nice -n -20 – /home/pi/airspy_adsb -l 30005:beast -b -x -m 12

No -p (USB bit packing)?
Also, nice -20 is very weak. Wasn’t that supposed to be --20? As in two - signs before? Dump1090 runs with -5

Redundant when using -m 12.

-20 is actually the highest possible priority.

It shouldn’t matter much if the priority is -5 or -20.

Thanks for the explanation.

Not that i have a airspy yet that will have to wait some.
But if someone asks on this forum i can better explain the command line options or reference this thread.

If you tweak the command line anyway it would probably make sense to document the defaults somewhere, in the help for example.

Sure and thank you. It’s a real challenge to do any useful DSP at these rates in a computer like the RPi, and that’s just half of the problem. The RPi (when running Linux) is not a real-time system and sometimes the kernel just delays the processing the IOs for a while, which could result in a loss of packets. There are many mechanisms in place to compensate for this loss to keep the MLAT counter as accurate as possible, but the end user should understand the limitations of the RPi platform. Another issue is that the USB controller is on the same bus as the Ethernet controller (which presents itself as a USB device as well …) This means you will hit a hard limit of usable bandwidth if you run the decoder at 20MSPS without packing in parallel with another program that streams data over Ethernet (like a web interface).
In general, everything was optimized to the bone and the defaults “just work”. It’s a miracle it works at all.

Actually you can circumvent that by using WiFi which is kinda crazy.
The wifi chip is not connected via the USB hub.

Anyway i’m running my “old” laptop (an lenovo x230) as a server.
After using powertop --autotune the thing goes down to 8W which is really acceptable.
So if i were to get an airspy i would probably run it off that laptop :slight_smile:

Not bad at all for a laptop! The typical CPU usage on a RPi3 with -m 12 is 50% of one core at 1.2 GHz, so it should use a smaller fraction on Intel CPUs.

I was saying that the nice command needs also one “-” for option separator. For example, it should be “nice --5” to set it to -5. His example would set it to 20.
I did set mine to -5, same with dump1090-fa.

No it wouldn’t. There is a -n before the -20.

-n, --adjustment=N
              add integer N to the niceness (default 10)

Sorry, now I see. My nice command has no -n.
https://www.lifewire.com/uses-of-commands-nice-renice-2201087

This only works if you are using the package addon version of piaware/dump1090-fa
Also dump1090-fa needs to be configured to net-only so it will start without a dongle.

So while the thread might be confusing because it went through some trial and error, your post isn’t much help either.

The page you cite is wrong. 1090MHz ADS-B messages have a 1Mbps bitrate; the typical bandwidth is ~2MHz; the specification’s spectrum limits require -3dB at +/-1.3MHz around 1090MHz. I don’t know where they got 50kHz from.

Bless your heart. I am out of here.

I thought that 1.3MHz bandwidth was only for ADS-B “In” with UAT option?

From Annex 10 vol IV:

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