|
|
Single SideBand Modulation |
|
Single Sideband
Suppressed Carrier (SSB-SC) modulation
was the basis for all long distance telephone communications up until the
last decade. It was called "L carrier." It consisted of groups of telephone
conversations modulated on upper and/or lower sidebands of contiguous suppressed
carriers. The groupings and sideband orientations (USB, LSB) supported
hundreds and thousands of individual telephone conversations.
Due to the
nature of SSB,
in order to properly recover the fidelity of the original audio, a pilot
carrier was distributed to all locations (from a single very stable frequency
source), such that, the phase relationship of the demodulated (product
detection) audio to the original modulated audio was maintained.
Also, SSB was used by the U.S. Air force's Strategic Air Command (SAC) to insure reliable communications between their nuclear bombers and NORAD. In fact, before satellite communications SSBwas the only reliable form of communications with the bombers. The main reasonSSB is superior to AM, and most other forms of modulation is due to the following:
SSB
verAM
Example:
A HAM running 2000 Watts AM,
would sound no better than another
|
See also: AM---DSB---FM---QAM---Mix & Mod |