Quick update thanks to the long week end in France which left enough time to test all
combinations of hardware and software:
1/ I tried applying the patch provided by Steve on this list on librtlsdr and compiling
gr-osmosdr for running in gnuradio-companion. I know I am running the right source block
linked with the right library (added debug messages) => no signal on a R820T2 dongle
connected
to a signal generator (I+), the other pin (I-) either grounded or decoupled with a 100 nF
cap.
2/ doing the same on a E4k based dongle also provided only noise and no signal, a strange
result
since in the very beginning of my experiments (2012) I had used this same dongle for
direct
sampling. Being a zero-IF, I could just bypass the E4k mixer and record the raw samples
fed to
I+ and Q+ (I- and Q- being grounded). Surprisingly, running the same gnuradio-companion
flowgraph (osmosdr source -> Qt time sink) with NO direct sampling option does yield
correct
samples, so the hardware is sound and functional.
3/ E4k no longer being available, I have to find a way to compensate for the R820T IF: I
checked
using no option in osmosdr source that I could get some relevant signal when tuning the
signal
generator around the IF frequencies (4.8 MHz ? 5 MHz ? difficult to say with all the
aliases), while
the option "rtl=0, direct_samp=1" always returns noise.
I am not familiar enough with the RTL2832U configuration registers to mess with them
myself, but
I believe direct sampling in not functional at the moment in librtlsdr. I might be wrong
of course.
Thanks, JM
--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe, 25000
Besancon, France