User talk:Alinja

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Modulation techniques
Hi there - I know you have been on Wikipedia for a while, but I wanted to welcome you to the project! I noticed your comment on the modulation techniques template. Do you think there are other templates that would be useful too? Cheers, --HappyCamper 11:23, 21 June 2007 (UTC)

Question
You made changed the following text in the Eb/N0 article:


 * For a PSK, ASK or QAM modulation without pulse shaping, the B/fs ratio is slightly more than 1. With raised cosine pulse shaping, the ratio may be slightly larger than 0.5.

to
 * For a PSK, ASK or QAM modulation with pulse shaping such as raised cosine shaping, the B/fs ratio is usually slightly larger than 1, depending of the pulse shaping filter.

You wrote the following comment: B/fs is always more than 1, and there's always at least an implicit pulse shaping filter.

According to Nyquist, or Hartley's law, the symbol rate can be twice the bandwidth. Is this only valid for low-pass signals and equivalent baseband signals?

Kindly Mange01 12:59, 17 July 2007 (UTC)


 * Yes, I suppose that a baseband signal bandwidth can be one half of the symbol rate. ASK can be described as a real valued baseband equvalent, but when modulated it has a symmetric spectrum and bandwidth >= symbol rate. For QAM, the baseband equvalent is complex and spectrum is not symmetric wrt zero frequency, so it may not be fair to call zero-to-max-frequency the bandwidth. I'm not sure about PSK if it's implemented as true phase modulation. Maybe the sentence could be re-written in a clearer way. Alinja 08:51, 30 July 2007 (UTC)

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