Re: [Discuss-gnuradio] Failure of sending square wave over USRPs (back-to-back)

[Sylvain Munaut]

Hi,


> I try to send square wave from one USRP to another.
> The received signal at the receiver USRP is very different from what
> was being sent.

> This is just a very simple setup. What could be wrong ..?

Apparently your understanding of how things work :)

First thing, square waves have infinite bandwidth, the DAC can't
generate them properly, the ADC can't capture them properly and
they'll be modified by the IF filters. The effect of that is to "round
off the edges". And since you sample at 32k, that's probably going to
be fairly visible.

Then the second and major thing is that I & Q aren't magically
transmitted and received perfectly aligned. Unless you use the _exact_
same totally phase aligned LO and ensure the propagation delay to have
the ADC sample exactly on your DAC transmitted symbols, the I & Q you
receive won't be the I & Q you transmit, you'll have random time and
phase alignement.


That's kind of why people use modulation rather than TX raw binary waveforms.


Cheers,

    Sylvain