RTL-SDR dropping samples, RT throttling problem?

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1

I’m attempting to use a RTL-SDR stick on my BBB, but too many samples are being dropped to be stable. When running the test program rtl_test, a typical output is like this:

Sampling at 2048000 S/s.
Reporting PPM error measurement every 10 seconds…
Press ^C after a few minutes.
Reading samples in async mode…
lost at least 68 bytes
real sample rate: 2048506 current PPM: 248 cumulative PPM: 248
real sample rate: 1613474 current PPM: -212171 cumulative PPM: -108885
lost at least 33108 bytes
[snip]
lost at least 33820 bytes
lost at least 568 bytes
real sample rate: 2231729 current PPM: 89712 cumulative PPM: -42138
real sample rate: 2047938 current PPM: -30 cumulative PPM: -31448

A perhaps telling dmesg output occurs when I start the test program:

sched: RT throttling activated

The same stick has no problem on my laptop and a Raspberry Pi. I’m running debian jessie and I tested kernel kernel versions 3.8.13-bone67, 3.14.23-ti-r34, and 3.18.0-rc5-bone1 which all had the problem. Any thoughts?

2

Hi Adam,

I’m thinking of doing an RTL-SDR project with the BBB, as well. Sorry I can’t lend any advice, yet, since it’s just concept stage for me right now. I may have some insight in a week or two since a satcom project here in NYC may be moving from using the RPi to the BBB.

Have you had any further success with your BBB setup? Would you mind telling me which stick you’re using?

Thanks much.
Charles

3

I haven’t had time to further troubleshoot this problem, sorry.

The stick I’m using is some random stick I picked up cheap on amazon from china.

rtl_test identifies as:

Realtek, RTL2838UHIDIR, SN: 00000001
Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner

lsusb identifies as:
ID 0bda:2838 Realtek Semiconductor Corp. RTL2838 DVB-T

I did find a premade image for doing RTL-SDR stuff on the BBB here, which sounds promising:

http://www.kd0cq.com/2014/08/packed-full-beaglebone-black-img-file-rtl-sdr-gnuradio-gqrx-lots-more-on-ubuntu-14-04/

4

Hi Adam,

I’m going to plow on and get a dongle anyway. I’ll plan to report back here in a couple of weeks. Thanks much for the link, which looks like a monster time-saver.

Charles