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[Discuss-gnuradio] Lost samples from RTL2832 dongle

From: john cooper
Subject: [Discuss-gnuradio] Lost samples from RTL2832 dongle
Date: Tue, 23 Jan 2018 12:40:13 +0000

Hello GNU people, some help greatly appreciated.

I am a newbie to GNU Radio and have a lost samples problem,  lost from the USB 2  RF device, seemingly not in the Flowgraph signal chain.

Although I have no hard evidence I am coming to the point of suspecting the problem lies with the running of GNU under Oracle VM,  hosted by Win 10.

Physical RF device is a  DVB-T+DAB+FM USB dongle, with Realtek RTL2832U and the R820 device.

System is GNU Radio ( latest version )  running as a guest under Oracle VM, hosted by Win 10 Pro on a machine with significant system resources.

Oracle version is VM 5.2.6r

Problem is *always* dropped samples from a DVB-T+DAB+FM USB dongle, tens to hundreds of lost samples.

I have done the following :-

    Added my name to the virtualbox users list.

    added the Virtual Box Extension Pack 5.2.6     to allow USB 2 support in the VM

    Selected USB2 in the Oracle VM machine.

    Blacklisted the RTL2338 DVB-T  driver  via   /etc/modprobe.d/blacklist-rtl.conf    etc.
    Tested with rtl_test with sample speeds from 2.4e6 down to 0.25 e6

    Several Flowgraphs of various example FM broadcast receivers all have choppy audio, believed to be due to lost sample from the RF device via USB2 and not seemingly due to mismatch of audio sing sample rates.

Using only the RTL_SDR source block and Low Pass Filter, plus the WX GUI FFT Sink and the WX GUI Scope Sink, in a FlowGraph produces spikes in the Audio which coincide with the suggested sample losses from the physical dongle.

Under any and all tests and sample rates the result of rtl_test when ran in the terminal is a continual stream of lost samples.

Other information;

running SDR# via the host system ( Win 10 Pro )  is faultless at 2.4e6 sample speed and all lower speeds.

I have also  installed Gqrx in the VM and this system stalls with the Terminal screen failing to enter the initial set up dialogue screen but does list in the terminal screen the list of parameters, then hangs.

If anyone has input to the problem, I would be very pleased to hear back and offer my thanks in advance.


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