[Discuss-gnuradio] Interpolation in usrp_siggen

[Shyamnath]

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
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