Spyserver+RTLSDR

[Antoine Roquentin]

Hi,
I'm new to radiosonde rxing.
I managed to set up spyserver on linux with an RTLSDR dongle.
I noticed that i only get about 2-10 packets uploaded per upload, despite a good SNR of 20-25 dB.

When I use auto_rx directly with RTLSDR, I get >15 packets per upload.

Is there anything that I can/should do?

Thanks

[Mark Jessop]

This possibly suggests a CPU issue, resulting in dropped samples. You could use the 'top' command to see if your CPU is getting overloaded.

What sample rate are you running the RTLSDR at, and what machine are you running this on?

I wouldn't necessarily recommend using a RTLSDR with SpyServer, since a RTLSDR doesn't have enough bandwidth to cover the radiosonde band by itself. Depending on where you are in the world, either an Airspy Mini (4.8 MHz coverage) or Airspy R2 (8 MHz coverage) would be required. 

If you're having dropped samples issues with a RTLSDR then you would likely have similar issues with an Airspy however.

73

Mark VK5QI

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[Antoine Roquentin]

I do indeed have a lot of CPU load, but most of it running at lowest priority (nice 19). load average: 5.30, 6.51, 8.36
CPU is i5-4690K.
In the spyserver window i don't see anything regarding dropped samples.

The RTLSDR is at default sample rate, I think which is 2 MHz. The bandwidth is just enough (for now :) to cover the two nearby launch sites. 
I'd have an RSP2 with 10 MHz bandwidth, but I think it is not supported by spyserver.

[Antoine Roquentin]

I killed the other tasks and it seems to be independent from CPU load.

[Mark Jessop]

Unfortunately I'm not sure what the issue is then. An i5 should easily be able to handle this.

RTLSDR's aren't very well supported in SpyServer (the dev wants to sell Airspy units I guess...), so there may be some other issue going on. Spyserver error messages are pretty lacking, and I don't think you get any indication of buffer under/over-runs anywhere which would show this kind of problem...

Sorry I can't be of more help :-(

73

Mark VK5QI

[Antoine Roquentin]

One thing that i found: When the RTLSDR is aquired by spyserver, i get these messages:
Device was sleeping. Wake up!
Found Rafael Micro R820T tuner
[R82XX] PLL not locked!
Acquired an RTL-SDR device
Allocating 15 zero-copy buffers

I would have assumed that the "PLL not locked" happens only during start up, but who knows. Do others have this message too?
In SDR#, connected to spyserver, the signal looks good and there's no audio glitches or such.

[Mark Jessop]

Those messages are fairly 'normal' for RTLSDRs. You see those on rtl_fm and rtl_power.

Cheers,

Mark

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[Antoine Roquentin]

I somehow got it working by moving the center frequency slightly. Now I also have 15/16 packets per upload.

I see 4 slightly weaker mirror signals of the same radiosonde across the entire spectrum, perhaps it was overlapping with itself. 

I don't know yet why i have those mirror signals with spyserver, I don't have them when I use gqrx.

[Antoine Roquentin]

Oh, and the SNR is about 6-7 dB worse with spyserver than when using rtlsdr directly.
It's good enough, I still have a bit margin. But I hope spyserver will be working better with airspy :)