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


From: Josh Blum
Subject: Re: [Discuss-gnuradio] 4x RX chains on USRP1 with DBSRX2
Date: Tue, 12 Feb 2013 20:23:18 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130106 Thunderbird/17.0.2


On 02/12/2013 04:03 PM, Marcus D. Leech wrote:
>>
>> 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
>>
> Also, will he need to use the 4rx FPGA image, or will UHD automagically
> use the right image?
> 
> 

Its an args option, exact example here:
http://files.ettus.com/uhd_docs/manual/html/usrp1.html#specify-a-non-standard-image

-josh

> 



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