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

From: srinivas naga vutukuri
Subject: [Discuss-gnuradio] The sinusiodal waveform is drifting from input to output.
Date: Wed, 03 Mar 2010 16:56:34 +0530
User-agent: Thunderbird (X11/20090817)


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,

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