Popping noises

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Remon
Posts: 43
Joined: Fri Jun 22, 2018 2:49 am

Popping noises

Post by Remon » Sat Aug 18, 2018 2:02 am

Does anyone else have popping noises during listening? It sounds like a recording with a microphone without wind screen / pop filter. I do hear it mostly on the 70 cm band. I can hear it during transmissions but also with static noise while there is no signal. With audio filtering enabled the popping noise is almost reduced to zero but I don't like listening with filters. It seems to only appear on NFM. With other modes I don't hear the noise. I already tried different USB cables, coax cables and antennas, moved away the antenna from the RTL-SDR, moved the RTL-SDR away from the computer etc etc. Sometimes it also start giving clicking noises which are also visible on the waterfall. Restarting SDR# solve the latter problem.

I also have a second RTL-SDR as a spare which has none of the issues described above.

rtlsdrblog
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Joined: Mon Nov 19, 2012 11:54 pm

Re: Popping noises

Post by rtlsdrblog » Mon Aug 20, 2018 12:22 am

What sample rate are you running at? If it's anything more than 2.4 MHz the dongle will randomly drop samples, which could explain the popping sound.

Remon
Posts: 43
Joined: Fri Jun 22, 2018 2:49 am

Re: Popping noises

Post by Remon » Mon Aug 20, 2018 12:42 am

I'm running the dongle at 2.048 MSPS over a local LAN network with rtl_tcp.

I'm currently testing my spare dongle for 2 days with no issues at all. This is the rtl_test output after letting it run for 5 minutes from the dongle without problems:

Code: Select all

[email protected]:~/rtl-sdr $ rtl_test
Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Supported gain values (29): 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
[R82XX] PLL not locked!
Sampling at 2048000 S/s.

Info: This tool will continuously read from the device, and report if
samples get lost. If you observe no further output, everything is fine.

Reading samples in async mode...
Allocating 15 zero-copy buffers
lost at least 132 bytes
And this from the dongle with the popping sounds:

Code: Select all

[email protected]:~/rtl-sdr $ rtl_test
Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Supported gain values (29): 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
[R82XX] PLL not locked!
Sampling at 2048000 S/s.

Info: This tool will continuously read from the device, and report if
samples get lost. If you observe no further output, everything is fine.

Reading samples in async mode...
Allocating 15 zero-copy buffers
lost at least 176 bytes

rtlsdrblog
Site Admin
Posts: 1859
Joined: Mon Nov 19, 2012 11:54 pm

Re: Popping noises

Post by rtlsdrblog » Wed Aug 22, 2018 12:36 am

It's probably an rtl_tcp issue then. Perhaps the network is dropping samples, or the machine running the dongle isn't powerful enough? Maybe try an alternative server like SpyServer and see if the same issues persist.

Remon
Posts: 43
Joined: Fri Jun 22, 2018 2:49 am

Re: Popping noises

Post by Remon » Wed Aug 22, 2018 1:08 am

I can test it but I can tell you in advance that rtl_tcp use much less CPU load than SpyServer. My Raspberry Pi 3B+ is idling 98.8% at all times.

rtlsdrblog
Site Admin
Posts: 1859
Joined: Mon Nov 19, 2012 11:54 pm

Re: Popping noises

Post by rtlsdrblog » Thu Aug 23, 2018 10:53 am

It's not about the CPU usage (as long as it's not being CPU limited). rtl_tcp often has some problems, maybe bugs, that causes drops to occur sometimes.

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