Single Sideband Suppressed Carrier (SSB-SC):
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 SSB-was the only reliable form of communications with the bombers.
The main reason-SSB-is superior to-AM,-and most other forms of modulation is due to the following:
SSB-ver-AM
(1) Since the carrier is not transmitted, there is a reduction by 50%
of the transmitted power (-3dBm). –In AM @100% modulation: 1/2 of the power is comprised of the carrier; with the remaining (1/2) power in both sidebands.
(2) Because in SSB, only one sideband is transmitted, there is a further reduction
by 50% in transmitted power (-3dBm (+) -3dBm = -6dBm).
(3) Finally, because only one sideband is received, the receiver’s needed
bandwidth is reduced by one half–thus effectively reducing the
required power by the transmitter another 50% (-3dBm (+) -3dBm (+) -3dBm = -9dBm). –Remember, if a receiver’s bandwidth can be reduced by 50%: the needed transmitter power is also reduced by 50%, i.e., the receiver’s Signal to Noise Ratio (SNR) is improved as the receiver bandwidth is reduced. This of course implies that the signal containing the information is not lost–which is the case in this instance. –Huh? Its true: if I’m Lying, I’m Dying!
Example: A HAM running 2000 Watts AM, would sound no better than another
HAM running 250 Watts PEP (Peak Envelop Power) on-SSB.
