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

From: Douglas Geiger
Subject: Re: [Discuss-gnuradio] Single-tone test using USRP2 with RFX2400 and XCVR2450
Date: Fri, 28 Aug 2009 11:56:56 -0400

On Fri, Aug 28, 2009 at 11:09 AM, Igor Almeida<address@hidden> wrote:
> I [believe I] am having a similar problem with USRP rev4 and RFX2400.
> Sending a QAM-modulated signal in a 2.5GHz carrier with no
> synchronization gives me a lot of background noise before the actual
> signal. So I am prepending a 2MHz sine wave in a separate block,
> executed prior to the QAM modulation, but I cannot find the impulses
> in +- 2M after the receiving USRP downconverts it from 2.5GHz.
> The part of the signal which is supposed to contain the 2M wave shows
> both real and imaginary sinusoidal signals, always close to DC by 3k
> Hz or so. Am I missing anything?
> --
> Igor Almeida

That sounds like it could be a frequency offset between TX and RX. You
say you aren't synchronized (which I interpret to mean you don't lock
the clocks of the TX and RX together somehow) - do you have a costas
or similar carrier offset recovery block/process on your receiver?

Doug Geiger

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