Re: [Discuss-gnuradio] calculated vs observed pulse length

[seph 004]

Matt Ettus <address@hidden> wrote:
>   seph 004 wrote:
> >  This would mean that to obtain a total rate of 32 Msamples/sec to the 
> > DAC, the data rate of the I and Q channels would have to be 16 
> > Msamples/sec each, and thus 128 000 samples/sec each into the txchain 
> > modules. This should mean that if I provide a samples set of 128 I 
> > samples, and 128 Q samples, I should get 1 msec worth of complex 
> > output signal.
>
> The bus carrying IQ data to the 9862 TX runs at 64 MHz, so it is 32 MS/s 
> for each.
>
> Matt
Thanks for the reply.
  
  I see what you are saying about the bus. It means that the pulse is  longer instead of shorter, which makes more sense. Going with this  though, I have done tests with the new numbers and I still get a longer  pulse than expected. I
 thought the problem might have been a delay from  the cic shifter or the DAC, but even those should only have added a few  microseconds, not over 100 microseconds. 
  
 From the logic  analyser , it seems that the counter I use for advancing the read  pointer for the RAM might be running slow, though the Quartus simulator  shows it running at the right speed. Would such a problem stem from  using an interp rate like 125 within the FPGA? Has anyone who has done  USRP FPGA builds that use counters noticed a similar variance?
  
  Regards
  
  Lance

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