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Re: [Discuss-gnuradio] Carrier leakage on transmit

From: Charles Brain
Subject: Re: [Discuss-gnuradio] Carrier leakage on transmit
Date: Tue, 25 May 2010 15:40:45 +0100

Well I have had another look at the offset stuff.

What seems to be happening is that when you apply an offset you have to scale back the max IQ values being sent to the USRP2.

I get this situation.

No LO offset, great raised cosine shaped QPSK signal
Add LO offset, QPSK signal looks awful.

Reduce IQ signal amplitude QPSK signal again looks good and I can see the LO offset on the spectrum analyser.

I have also noticed that when I try OFDM the unwanted rubbish on either side of my OFDM signal changes with LO offset.

There seems to be an interaction in there somewhere probably
to do with the complex mixer in the FPGA. I have not ruled out my own code yet but it seems unlikely.

- Charles


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