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Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XC

From: Igor Almeida
Subject: Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
Date: Fri, 28 Aug 2009 17:31:49 -0300

On Fri, Aug 28, 2009 at 5:22 PM, Eric Blossom<address@hidden> wrote:
> If you're trying to send a sine wave, this will work much better:
> (Generates a complex sinusoid == exp(jwt))
>  sig_source_c -> head -> usrp.sink_c
> Or you could use a hilbert transform to generate the quadrature
> component.  float_to_complex will be setting Q to zero the way you're
> using it.

Yes, setting Q to zero was the original idea. The whole point of using
a sine wave was to have a better estimation of when the QAM signal
actually started, but this "solution" gave me another problem to work
on :)
My question is why the received signal has sinusoidal components on
both I and Q given that the wave has been "translated" to 2.5G (upon
tx) and then back to DC (after the FPGA in rx). Should I not expect
two impulses at +- 2M? Instead, what I get is a single impulse at
aproximately -3kHz, regardless of the frequency set on the sig_source.

> Eric

Igor Almeida

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