From: Dave on Wed, Aug 30 2006 10:34 am


Let me digress into another of your questions: i.e. What is SSB?

Fifty years ago ham radio, and still today the AM broadcast band, transmitted
three components to put a signal on the air. First, was the carrier that set the
dial frequency e.g. 3950 KHz. The carrier contains NO information, it just sets
the dial frequency. Then voice audio was added to the carrier. This addition
[modulation] produced two audio signals around the carrier. One above the
carrier, the other below the carrier. So, the resulting signal had the carrier
and one upper side band and one lower sideband. The carrier contained 2X the
power of the audio. And the audio was redundant with 1/2 the audio power in each
sideband. The resulting signal can be described as Double Sideband Plus Carrier.

In the 50s and early 60s design techniques were incorporated to suppress the
carrier, which contained NO information; and to eliminate one of the redundant
sidebands. The resulting signal is Single Sideband [one audio channel] with
suppressed carrier. [SSB = Single Side Band]

"Dave," your knowledge of Single Sideband is ferklempt.

The spectra of an amplitude modulated signal was mathematically
described by John R. Carson of AT&T before the 1920s. SSB,
including suppressed carrier, was USED by the telephone
infrastructure in the 1920s for long-distance lines. The most
common system, "C Carrier," had four separate 3 KHz voice
channels and would operate on the open-wire telephone lines
then common all over the world. This "C Carrier" was directly
adapted to HF radio in the early 1930s, the frequency-multiplexed
total signal converted to HF and amplified. The first HF SSB
radio link was put into service between the Netherlands and the
Netherlands Antilles carrying four voice channels or (to become
the later commercial-military standard of two voice and six to
eight TTY channels). While single-channel SSB was experimented
with before WW2, it didn't expand until after WW2 and a number
of US military contracts awarded to then-prominent radio makers
(Collins, RCA as two examples). Based on that success, the
amateurs took it up in the 1950s while the ARRL promoted the
false idea that "SSB was pioneered by radio amateurs."

Technically, your statement was faulty. Each "sideband" (the
spectra adjacent to the carrier) carries ONE QUARTER of the
total RF power output of single-channel SSB, not "half" in
normal AM. In normal AM the carrier is always constant in
amplitude. In normal AM receivers the "detector" stage is a
mixer, combining the carrier with the two sideband spectra
with the output lowpass filtered to yield the original audio
signal. Single-channel SSB usually suppresses the carrier
(almost to extinction) and the "detector" stage being fed an
equivalent constant-amplitude carrier signal from an internal
receiver oscillator. The mix products of carrier re-insertion
and the input single sideband spectra yield the original audio
modulation after lowpass filtering.

The important thing about single-channel SSB is that a
transmitter peak power output of RF need only be one-half
to on-quarter of a conventional AM transmitter to yield
the same demodulated audio signal level.

No morsemanship skill is necessary to use a single-channel
SSB radio. Today it is being used on the open sea by
both commercial and private boat/ship owners for voice
communications; also data, separate or multiplexed, for
written communications.