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
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.
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
most other forms of modulation, is due to the following:
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.
in SSB, only
one sideband is transmitted, there is a further reduction
by 50% in transmitted power (-3dBm (+) -3dBm = -6dBm).
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?
true: if I'm Lying, I'm Dying!
A HAM running
2000 Watts AM,
would sound no better than another
250 Watts PEP (Peak Envelop Power) SSB.
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
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
I had 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
In Fact to take advantage
of this, I built an acoustic delay-line which delayed the audio to one
ear ~16 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!
It worked best with
head phones, but it worked well with speakers also. 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 taxing during poor reception.
 The acoustic
delay-line used about sixteen feet of 3/16" neoprene tubing, driven at
one end by a 16 ohm, electromagnetic ear bud. At the other end was a (piezo)
crystal ear bud with a gain stage to make up for the -50 dB inherent loss.
The frequency response of the overall system (300 Hz to 2400 Hz) was dictated
by the receiver's SSB mechanical filter.