r820t2 based receiver raw samples ?

Jean-Michel FRIEDT jean-michel.friedt at femto-st.fr
Fri Oct 28 06:07:17 UTC 2016

I am attempting to use a RTL2832U based DVB-T dongle as a "fast" ADC
for recording baseband signals. gr-osmosdr under GNURadio 3.7 (as provided
by Debian GNU/Linux) provides the expected samples when using an E4000 (zero
IF) dongle. Being obsolete, such a dongle is no longer relevant, and I want
to do the same with the (non-zero IF) R820T(2) dongles. From
http://sdr.osmocom.org/trac/wiki/GrOsmoSDR I should be able to use the
direct_samp=1|2 option, but that does not work. I kept pins 1 and 2 connected
to the R820T output and connected a wire to pin 5 (Q-) while Q+ (pin 4) is
short circuited to pin 3 (gnd). A signal generator outputs a periodic signal
(150 mV amplitude, 100 kHz) but still no baseband signal, and on the FFT
of the osmosdr output I still see the spectrum of the FM band when tuning
to 100 MHz rather than the samples from the (initially unconnected) Q input.
Any idea if the "Device Arguments" of osmosdr-source is actually parsed
and interpreted ? or is there a command line way of acquiring the raw baseband
I/Q data ?

Thanks, JM

JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe,  
25000 Besancon, France

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