Posted by Zak on 10/27/06 20:29

Lawrence D'Oliveiro wrote:

> However, decoding an SSB signal involved a lot of complicated analog
> circuitry to reconstruct the missing sideband and carrier before the result
> could be demodulated as a normal AM signal. So analog TV, instead of
> completely getting rid of the second sideband, simply cuts it down to
> a "vestigial" sideband. Apparently this is enough for conventional AM
> demodulation circuitry to work, while still managing to cut the amount of
> bandwidth needed for an analog TV channel by nearly half.

SSB decoding only works if the frequencies of the output don't matter.

TV used Vestigial Sideband: the carrier is transmitted, but most of the
lower (?) sideband is cut off.

The receiver cuts off at the carrier frequency. The carrier is reduced
by half, whatever was transmitted in the lower sideband to nothing. The
result is that the carrier is in the correct ratio to the remaining
sideband.

If you mistune a receiver the result is more or less contrast. This is
caused by the varying ratio of carrier energy to sideband energy.


Thomas

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