Re: [Discuss-gnuradio] Sampling Freq

[David Scaperoth]

On Mar 22, 2007, at 5:11 PM, Jonathan Shan wrote:

> On Thu, 22 Mar 2007, Johnathan Corgan wrote:
>
> > Jonathan Shan wrote:
> >
> > > When I send this to file_sink, I see correctly 16 samples from  
> > > peak to
> > > peak. However, when I transmit this using 'usrp sink' and receive  
> > > at the
> > > other end, I see about 32 samples from peak to peak.. double what I
> > > expected. What is happening?
> >
> > What do you have the transmitter interpolation and receiver  
> > decimation
> > set to?
>
> interp_rate = 64, decim_rate = 16.

FWIW:

16 samples per cycle and interp = 64 (2MSps over the USRP) means  
sinwave freq = 2MSps/16 = 125kHz
32 samples per cycle and decim = 16 (4MSps over the USRP) means  
sinwave freq = 4MSps/32 = 125kHz


> I saw the formulas
> usb_sample_rate1 = 64e6 / decim_rate
> usb_sample_rate2 = 128e6 / interp_rate
>
> Using current values, usb_rate1 = 2 * usb_rate2. I'm assuming.. to
> get the correct sampling freq, usb_sample_rate at both ends should be
> same?
>
> Jonathan Shan
>
>
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