GRC: sending IQ samples of square is resulting with lot of noise

Hi,

I am using Gnu Radio Companion, and USRP2 RFX1800 daughter card. I
created on Tx end: a File source and USRP2 sink, and on Rx End: created
USRP2 Source and A File sink. The two USRP2’s are connected with RF
cable with attenuator, to see under less noise conditions the trials and
are separated by around 2-3 meters.

Am sending a +1 to -1 amplitude square wave samples from Tx and when i
capture on Rx end its not almost a square wave. I have generated the
above .py scripts using grc. Kindly help me out in correcting the above
scripts, if am not correctly done, As a newbie to gnuradio.

At least i got some wave form on the rx end. But when i try to execute
the tx_samples, rx_streaming_samples, i did’t even got this result for
the same Interp and decimation factor, what am making mistake in the
experiment?. And am using the encode.cc and decode.cc to encode IQ
samples text file and decode the samples into I Q form, to
analyse in the gnuplot(MATLAB,etc). Can also see the files here.

best regards,
srinivas.

On Wed, Jan 27, 2010 at 3:31 AM, srinivas naga vutukuri
[email protected] wrote:

Am sending a +1 to -1 amplitude square wave samples from Tx and when i
capture on Rx end its not almost a square wave. I have generated the above

I believe this is the maximum output power for the USRP2, and your are
likely seeing distortions from the non-linearity of the circuits
involved. I’m not sure what the linear range is for your
daughterboards, but try turning it down to +/- 0.3 and see what
happens.

Also, make sure that your decimation/interpolation factors are
correct. That is, if the DAC and ADC are operating at different
sample rates, you have to adjust your int/dec factors or samples per
symbol accordingly.

Jason

Thank you Jason, I could able to see the exact waveform of the samples
from One USRP2 to another USRP2. But i found the scaling of the
amplitude when I see from usrp2_fft.py and attaching a Scope Sink (like
oscilloscope scope sink), there is much variance, which usrp2_fft.py is
showing much amplified scale, but the real one of Scope Sink in the GRC
is showing very very low amplitude factor, Is there any understanding is
required here? And if i want to get some amplified result what to be
done?

best regards,
srinivas.

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