[Discuss-gnuradio] The sinusiodal waveform is drifting from input to output.

[srinivas naga vutukuri]

Hi,

I am transmitting the sinusoidal wave form (IQ samples), in the 
following methods, and found that when i stem plot in the MATLAB both 
the input wave form data on one USRP2 and the received data on another 
USRP2, initially the waveform is exactly fitting (i mean overlapping), 
and after certain samples, it starts ie., in the input wave form and the 
output data waveform drifting slightly and at the end samples both the 
waveforms overlaps perfectly. Why this slight drifting is happening when 
transmitting the I Q samples from one USRP2 to another USRP2.

1st method:

   I used, tx_samples.cc and receive_streaming_samples.cc.

2nd method:

  Using the GRC, created a signal source, and file sink and usrp2 sink 
on One PC and another PC usrp2 source and file source. So plotting both 
the input stored samples and output received samples, observed the above 
mentioned drift of mismatch of samples of the waveform and again at the 
end and start it perfectly matches or overlaps.


Kindly help me in understanding this phenomena, why this is happening on 
raw data (IQ) samples sending. But this never happens, when i checked 
with the benchmark_rx.py and benchmark_tx.py used (as internally these 
two are using GMSK modulation, sync work and packets framing method).


best regards,
srinivas.