Re: [Discuss-gnuradio] Using the USRP LFRX daughterboard to receive a complex baseband signal (I+Q)

[Eric Blossom]

On Sun, Feb 15, 2009 at 02:24:32PM -0800, Matt Ettus wrote:
>
>
> Josh Blum wrote:
>> The current USRP API does not support receiving complex signal (I on 
>> RXA and Q on RXB) from LFRX and BasicRX boards. At least not in an easy 
>> way...
>>
>> In the future, the USRP API will support complex samples, and  
>> "usrp_dual_source_x" will have an option called antenna: "RXAB"
>>
>> Any word on this from developers?
>
>
>
> We've talked about this in the past.  The quickest way to do this would  
> be to mod the LFRX code.  Currently it has 2 subdevices, one for the A  
> input and one for the B input, which control the mux settings.  If we  
> made a setting for a "C" input which just changed the mux settings, that  
> would solve it pretty quickly.
>
> Matt

You can get what you want today by just setting an appropriate value
for the Rx mux:

  /*!
   * \brief Set input mux configuration.
   *
   * This determines which ADC (or constant zero) is connected to 
   * each DDC input.  There are 4 DDCs.  Each has two inputs.
   *
   * <pre>
   * Mux value:
   *
   *    3                   2                   1                       
   *  1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
   * +-------+-------+-------+-------+-------+-------+-------+-------+
   * |   Q3  |   I3  |   Q2  |   I2  |   Q1  |   I1  |   Q0  |   I0  |
   * +-------+-------+-------+-------+-------+-------+-------+-------+
   *
   * Each 4-bit I field is either 0,1,2,3
   * Each 4-bit Q field is either 0,1,2,3 or 0xf (input is const zero)
   * All Q's must be 0xf or none of them may be 0xf
   * </pre>
   */
  bool set_mux  (int mux);


Assuming your Basic LF is on side A, this should work:

  u.set_mux(0x00000010)


Eric