Re: [Discuss-gnuradio] 4x RX chains on USRP1 with DBSRX2

[Josh Blum]

On 02/12/2013 12:10 PM, John Wilson wrote:
> Hi,
> 
> I'm wondering whether it's possible/how to use a USRP1 with 2x DBSRX boards
> to generate 4 separate streams via the 4rx usrp1 firmware. The required
> channels will be within the front end bandwidth of the DBSRX2.
> 
> At the moment I'm using a subdev spec of 'A:0 A:0 B:0 B:0' which I assume
> runs the signal from subdev A through RX chains 0 and 1, and subdev B
> through 2 and 3. Is this correct?

That seems correct.

> 
> I am planning to set each daughter board to a frequency between its two
> frequencies of interest, then I'd like the DDCs to downconvert the data
> from the ADC independently to sit the two frequencies of interest in the
> centre of their respective baseband channels out of the USB bus. So can I
> change the DDC frequencies independently of the centre frequency in the

You will want a tune_request object where the rf_freq is set to the
desired center frequency of the DBSRX (something in between that each
CORDIC can shift away from). And set the rf freq policy to manual.

There are some examples of making the tune request in the grc block for
usrp source properties dialog box.

> daughterboard? Also what is the resolution of the DDS in the DDC, i.e. can
> I tune each one independently in ~1Hz steps?
> 

The CORDIC resolution is pretty much 64e6/(1<<32), so sub Hz.


-josh

> Sorry if this has been asked before, I've been searching Google and the
> email lists all day and have not yet found an answer!
> 
> Thanks,
> 
> John
> 
> 
> 
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