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Re: [Discuss-gnuradio] SSB modulation with USRP2 Sink

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] SSB modulation with USRP2 Sink
Date: Mon, 20 Dec 2010 16:19:41 -0500
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On 12/20/2010 03:26 PM, Steve Mcmahon wrote:
Hello Marcus:

Thanks a lot for providing the GRC file. I did not realize it was so 
complicated to create a SSB-modulated signal. I thought it might be a parameter 
of the USRP2 Sink block.

So the USRP2 Sink will always generate a full-modulated (both upper- and 
lower-sideband) signal? Because it inputs complex values?

Steve McMahon
The USRP2/USRP1/N200/N210/E100/future hardware "knows" *nothing* about modulation at all. It faithfully reproduces whatever you give it in the complex stream going into it, and possibly both digital and analog up-converts it to the desired place in the
  spectrum, but it knows nothing about modulation at all.

Any time you mix two signals (multiply them), you end up with upper and lower sidebands. Conceptually, AM is a process whereby the modulation signal (audio) is simply mixed (multiplied) with the carrier and sent on its way. This produces the carrier and the two sidebands. With SSB (Single SideBand), you lop off one of those sidebands and the carrier.

There are a few extant methods for generating SSB signals--the so-called "filter method" is the one I've used in my flow-graph, since it's easy to understand once you realize that SSB is nothing more than a lobotomised AM signal. There is also the so-called
  "phasing" method which is used in analog SSB transmitters.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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