Re: [Discuss-gnuradio] USRP2 and Data Rate

[Garrett Wenger]

Marcus,
First of all, thanks for responding so quickly.  

I looked on the USRP2 faq and I did see that the DAC rate was listed as 400 MS/s, but later on in the faq it says:
    The FPGA talks to the DAC at 100 MS/s just like it talks to the ADC at 
100 MS/s. The interpolation from 100 MS/s to 400 MS/s happens inside the
 DAC chip itself. Unless you are doing something fancy, you can think of
 the
   
DAC as operating at 100 MS/s.

If I am just misunderstanding that and I do need to use 400 MS/s as my DAC rate, is there some upper limit to what the samples per symbol value can be? Since interpolation has to be between 4 and 512, the lowest possible values that I could use to get a 10kbps would be 80 samples per symbol with 500 as my interpolation rate. 

Thanks, 
Garrett

On Wed, Jul 7, 2010 at 11:45 AM, Marcus D. Leech <address@hidden> wrote:

On 07/07/2010 11:32 AM, Garrett Wenger wrote:
> Hi all,
> A few days ago I made a simple program using grc to fsk modulate and
> transmit a pn sequence at 10kbps. Since I was using a USRP1, I set my
> samples per symbol to 25 and the interpolation to 512 to get this data
> rate.
>
> The place I work at just received a couple USRP2's, so I am trying to
> get this same program working with the new devices.  I realize that
> the DAC rate for the USRP2 is 100 MS/s instead of 128 MS/s, so I
> changed the samples per symbol and interpolation rate to  25 and 400,
> respectively, but this does not give me the 10kbps rate like I
> expected it would.
>
> Is there something major that I am missing here?
>
> Thanks a lot,
> Garrett

Garrett:

The DACs on the USRP2 run at 400Msps, not 100Msps.  Although the *ADCs*
on the USRP2 do run
 at 100Msps, and that's perhaps where the confusion comes in.


--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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