Re: [Discuss-gnuradio] tuning the BasicRX board

[Eric Blossom]

On Mon, Dec 10, 2007 at 01:25:31PM -0500, George Nychis wrote:
> 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.

FYI, the spectrum isn't inverted on the basic_rx.

set_rx_freq(-10e6) should work, assuming you've got the mux setup correctly.

If you're using the first input on the Basic Rx on the A-side you'll
want set_mux(0xf0f0f0f0)

> 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.

The computation that splits the tuning between the RF front end and
the DDC is done in usrp.py (tune).  In the case of basic_rx, the
daughterboard set_freq returns (True, 0), indicating that DC is at 0
Hz in the IF.  That is, there's nothing to tune on the daughterboard,
and all the work is done in the DDC.

Eric