[Discuss-gnuradio] tuning the BasicRX board

[George Nychis]

Hi all,

As there is no solid C++ support for daughterboards yet, I'm attempting 
to tune the BasicTX/RX boards to use them in the meantime with the 
inband code.

I apparently have no issue tuning the TX board, as I can properly 
transmit some GMSK encoded data and use the standard python receiver 
(benchmark_rx.py) to decode it.  However, I am having issues tuning the 
RX board.

My goal is to tune the RX board to 10MHz.

The frequency of the DDC is set to -10e6 using set_rx_freq(), since the 
BasicRX board doesn't do quadrature downconversion and the spectrum is 
inverted.

Is there a default target frequency of the BasicRX/TX boards, as I do 
not think I can set it without C++ daughterboard control (i.e., a C++ 
equiv for set_freq())?  At the same time, looking at db_basic.py it 
seems as though set_freq() is an empty method, simply returning True on 
all calls.

I know my board is not properly tuned like benchmark_rx.py, as the raw I 
and Q values are on completely different scales when attempting to 
receive the GMSK encoded transmission.  Also, if I capture the raw 
samples using python code, and inject them in to my in-band receiver I 
can properly decode the transmission.  This means something is off below 
the GNU Radio level, down in to the USRP and daughterboard settings.

I'm fairly confident it is not an FPGA in-band implementation error, as 
I can properly transmit and receive a sine wave (by plotting it) using 
the code.

I'd greatly appreciate any help.

- George