Re: [Discuss-gnuradio] Interpolation in usrp_siggen

[Eric Blossom]

On Mon, Dec 11, 2006 at 08:30:25PM -0800, Shyamnath wrote:
> 
> hi,
> I am new to gnuradio architecture and am trying to learn about it. I was
> using the usrp_siggen,py sample code provided with different interpolation
> rates (4, 8,12,16,64)  since it has to be a multiple of 4.  the observations
> are as follows (which  cannot explain)
> 
> 1) For interpolation rates set to 4,8,12, at the sender, what I observe on
> the receiver (directly connecting the usrp_source to a file_sink), is just
> noise.
> 
> 2) For a interpolation rate set to 64, I almost get the required sinuosoidal
> at the required frequence(100khz), with the difference that the frequency of
> the signal at the receiver for nearly 200 samples at the beginning  is
> nearly 7KHZs. To understand this better, I just send a constant signal on
> the sender (using usrp_siggen.py) and received a sinousoidal at the receiver
> with a frequency of 7Khz (which I presume is because of the frequency
> offset). Although I think the above two observations are related I could not
> explain them.
> 
> 3) Another interesting case is when the interpolation rate is set to 16. the
> output at the reciver is a signal which has a sinousoidal with the required
> frequency(100khz) spaced with sinousoidals with a frequency of 7khzs.  This
> observation is something I cannot understand.
> 
>  Kindly help me out with this.
> 
> Thanks
> Shyam

You didn't mention which daughterboard you are using, but assuming
it's a Basic Tx, be sure to set the -f <freq> option to something like
10M.  Neither the Basic Tx nor Basic Rx will pass signals under about 100kHz.

Eric