posted on Apr, 5 2010 @ 12:51 AM
Originally posted by Donny 4 million
Please show how modulation causes sidebands in Amplitude Modulation.
Good Lord. That's all it does. If you are at 100% modulation, you will divert half the power into the upper and lower sidebands and half will remain
in the carrier.
That's why you get so much more bang for the final power by going with SSB - you get rid of the dead weight of the carrier, that's half the power,
and the sidebands just repeat each other, the same information's in both, so you get to put 75% more radiated power into one sideband in SSB, and
still meet the FCC's final power limits.
This is all standard comm theory 101.
The reason you use a non-linear stage for a detector like a multiplier or a diode is that it multiplies the sidebands and carrier (or local oscillator
in the case of SSB) which gives you the original signal as a baseband output.
As far as a link, go google "AM sideband modulation" or the like - there's hundreds of thousands of them. I'm not sure which one will catch your
fancy. But I'm not making it up. That's how it works. You see a lot of poop about envelopes with AM, that's a convenient but inaccurate way of
looking at it. What really happens is sidebands. If you've got a spectrum analyzer and an AM exciter, you can see them for yourself, it's really
instructive, or it was for me back when I was a lad.
The sidebands created by even a simple modulating waveform in FM or PM are many and varied. It's not nearly as simple as AM or SSB. If you plow
through the math they're where they're supposed to be, but it's nasty to do at first.