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Re: [Discuss-gnuradio] USRP DDC usage

From: Achilleas Anastasopoulos
Subject: Re: [Discuss-gnuradio] USRP DDC usage
Date: Thu, 26 May 2005 12:03:32 -0400
User-agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)

I have a question/observation on this issue:

Since the DDC multiplication is complex and since the internal DDC oscilator is noncoherent, I do not see a difference between the MUX settings: 0x33221100 and 0xf3f2f1f0.

Similarly, with the setting 0x00003210 you will never be able to
separate the two channels coming from ADC0/ADC1 and ADC2/ADC3.

Is this right?


On Wed, May 25, 2005 at 02:54:05PM -0400, Philip Balister wrote:

>> I'm working on making a SCA component for the usrp based on the usrp
>> standard interface. I've got a few questions on how to use the DDC's and
>> the input mux.
>> If I set the mux word to 0x33221100 (and the number of channels to four)
>> I believe I will have 4 channels of complex data from each A2D.

FYI, the current fpga image only support two DDCs.

You always get complex data out of the DDCs.  The question is what are
you putting in?

If you want two DDCs with a different pair of A/Ds to each one
the mux should == 0x00003210

>> If I set the mux word to 0xf3f2f1f0 I will have four channels of real
>> data, interleaved with the zeros from the Q channel.

Yes.  This will feed a zero to the Q input of each DDC and will feed
ADC's 3, 2, 1, 0 to the I inputs.  Note that there are only two
channels available in the current FPGA build.


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