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Re: [Discuss-gnuradio] USRP Tx Rate Conversion

From: Wireless Monster
Subject: Re: [Discuss-gnuradio] USRP Tx Rate Conversion
Date: Tue, 15 Apr 2008 15:14:45 -0400

Hi Brian,
Thank you for your help. Looks good :)

So If I understood correctly I can do the following:

I set the USRP interpolator to 64, so the USRP sink will consume samples at a 2MS/s. I add the resampler just before with a ratio 16/13 so I it consumes samples with a 1.625MS/s rate. Just before that I have the GMSK filter with a interpolation factor of 6 so at the input it is consuming samples at the desired rate 270833.333 Samples/s.

At hat point can I send the samples (for example from a file with gr.file_source) and guarantee they will be treated as a 270.8333Ks/s stream? (assuming there will be enough samples to process)

Thank you again for your help!

On Mon, Apr 14, 2008 at 8:55 PM, Brian Padalino <address@hidden> wrote:
On Mon, Apr 14, 2008 at 8:03 PM, Wireless Monster
<address@hidden> wrote:
> Hi All,
> I am new to gnuradio and the USRP board and I have a basic question.
> I want to transmit a GSM signal. Once It is encoded I have a  270833.333
> symbols/sec signal. Then, it is up-converted (x8) and GMSK filtered, so I
> get a 2.1666 Ms/s complex signal.
> Now the question: How to adapt this rate to the DAC converter on the USRP
> board?

Well, if you don't use your x8 upconversion, you can get away with a
rational resampling (I believe).

Taking 270833.333, and upconverting by 3x makes the sample rate
812500.  If you then rationally resample this by 16/13, you get a nice
1Msps signal which you can upconvert by a nice power of 2 for the

Try it out and let us know how it works out?


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