> 300 URLs WELCOME  to williamson-labs.com     --HOME > 90 Subjects on CD Single SideBand Modulation 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.    Anecdote: Back in the early 60s, when I was KX6AY (also KX6DB, and KX6BU) on Kwajalein, Island, in the Marshall Islands (PMR), I ran a 2 kW Collins S-Line SSB rig with a Telrex 6 element Tri-bander at 120 feet with the Pacific Ocean as a ground plane. :-).  Sometimes, on 20 meters, I would go down to the AM band (14,200 - 14,250 MHz), more often than not, I would hear only the carriers, no modulation--I kid you not!  I also ran a Collins KWM-2 (180 W pep) in my room with little trouble making contacts around the world.  I have often felt that there was even more advantages to SSB (than the 9dBm) due to the received signal's intelligibility (filtering, ability to tune off frequency changing pitch, etc.).  In Fact to take advantage of this, I built an acoustic delayline which delayed the audio to one ear ~27 ms more than the other, giving me a pseudo stereo like effect.  I could de-tune the receiver just a little and the effect was like placing different people in the QSO at different spatial positions within the room, with the receiver noise having its own spatial position--it was a hoot!  The effect of all this on top of improving the intelligibility, was to relieve a lot of the fatigue inherent in attempting to understand conversations in noisy environments over a prolonged time--which can be pretty severe during poor reception.    See also:    AM---DSB---FM---QAM---Mix & Mod ©  Copyright  2004  --  2006    Questions or Comments:  .   Suggestions are Solicited, P l e a s e !