Re: [Discuss-gnuradio] Transmit and Received Signals are Different

[Frederick Lee]

I figured out why the low pass filter was making the square wave look
like a sine wave. The square was represented by a Fourier series. In
other words, it was made up of many sine waves with different
frequencies. The Fourier Series for a square wave is: 4k/pi(sinx +
1/3*sin3x + 1/5*sin5x + ... ) When I applied the low pass filter with
a cutoff frequency of 1.1kHz to a 1kHz square wave, I was cutting off
the sine waves at the higher frequencies, (3kHz, 5kHz, etc.), so it
only showed the first sine wave in the series. If I set the cutoff
frequency of the low pass filter to 30 - 50 times the signal frequency
then I will get a fairly accurate square wave with some ripples on the
horizontal parts on the graph.

Here's the link to the pdf that shows this:
http://www.eecs.berkeley.edu/~boser/courses/40/labs/docs/UAF42%20square%20wave%20to%20sinusoid.pdf

As for the frequency offset, if I use the setup shown in the attached
flow graph ( this time with the taps being 1.0 + 0j ) and set the
frequency offset of the channel model block to 1m or less it looks
like a sine wave is being superimposed onto the square wave. I have
tried to filter out the low frequency sine wave, but that disrupts the
square wave. Is there a way to accommodate for the frequency offset
when transmitting and receiving between the USRPs?

Thanks,

Frederick

testing_channel_model.grc
Description: application/gnuradio-grc