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

[Activecat]

Dear Sylvain,

>On Fri, Mar 14, 2014 at 2:17 PM, Sylvain Munaut <address@hidden> wrote:
> 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".

I am using Ettus SBX daughtercard at the transmitter USRP to transmit
complex square wave (means the signal is in IQ form).
https://www.ettus.com/product/details/SBX
I understand that SBX performs quadrature up-conversion automatically,
and this feature cannot be disabled.
Hence, the signal sent to the transmitter antenna is no longer square
waves, but IQ up-converted signal.
That's why I guess the "round off the edges" effect is no longer
applicable here.

At the receiver side, another SBX daughtercard should have
automatically down-converted the signal back into IQ form.
Here I expect the signal output from SBX become (nearly) square wave.

> And since you sample at 32k, that's probably going to
> be fairly visible.

I repeat the test with sampling rate changed to 1MHz at both sides,
this gain similar undesirable result.

> Then the second and major thing is that I & Q aren't magically
> transmitted and received perfectly aligned.

Now I am focusing on the frequency and phase alignment issue.

Thank you very much.