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
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