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

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
http://www.sbrac.org

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