Intercom, Volume 5, Number 1, August 1971 Page: 15 of 16
16 p. : col. Ill. ; 28 cm.View a full description of this periodical.
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Tech Talk
SSB-Is it worth the additional cost?
By Bob Parsons
FCC Licensed Technician
Service Department 0804Few really understand precisely what
are the advantages (or disadvantages)
of Single Sideband (SSB) and Amplitude
Modulation (AM). To explain them,
definitions of a few terms are in order.
Carrier is defined as the radio fre-
quency, far beyond the audible range
of the human ear, which is developed in
the transmitter and radiated through
space by an antenna.
Modulation is the intelligence, de-
veloped in the human voice box, by
phonograph or by tape recording; or
tones produced by audio generators.
This intelligence is mixed with the
carrier, and radiated by antenna; the
modulation is then finally reproduced
in the receiver's speaker.
Sidebands are the result of the carrier
and modulation being mixed. There
are two sidebands-the upper sideband
(USB) which is the result of the carrier
frequency and modulation frequencies
being added and transmitted at fre-
quencies just above the carrier, and the
lower sideband (LSB) which is the
result of the modulation frequencies
being subtracted from the carrier fre-
quency and transmitted just below the
carrier frequency.
One should keep in mind the fact
that the sidebands contain 100 percent
of the intelligence. An AM transmitter-
a TRC-40 for example-transmits three
completely different signals at the same
time; these signals are the carrier, theM RF '
c
B
LSB USB
J\C
LSB, USB
D
US
LSB Eupper sideband, and the lower sideband.
As was stated previously, of these three
signals, only the sidebands contain in-
telligence. The carrier, on the other
hand, which uses 50 percent or more
of the total radiated power, can be
considered as wasted energy since it
contains no intelligence.
If we take away the carrier and apply
that wasted energy to the sidebands,
naturally the power of the sidebands
will be that much stronger. The Regency
Imperial does exactly that. This process
is called double sideband suppressed
carrier (DSBSC) - not true SSB, but
better than AM.
If you remove one of the sidebands
as well as the carrier, which can be done
due to the sidebands containing the
same intelligence, you can apply 100
percent of the transmitting power into
one sideband. This means a stronger
signal, for a given transmitter output
power, being reproduced in the speaker
of the receiver. It is possible that an
SSB transmitter can have as much or
more than three times the power of a
standard AM transmitter.
With these facts in mind, it should be
understood that the principal advantage
of the SSB over AM is that the power
of the intelligence is far stronger. Another
advantage is that, since there are no
carriers present when two or more SSB
transmitters are transmitting, there will
be no beat tones heard as in standard
AM transceivers. A third advantage isA: Shows the difference of modulation
and carrier frequencies
B: Shows a typical AM signal (TRC-40)
C: Shows a typical DSBSC signal; the
broken line shows the missing signal
D: Shows a typical USB-SSB signal; the
broken lines show the missing signals
E: Shows a typical LSB-SSB signal; the
broken lines show the missing signalsthat only one-half of the channel fre-
quencies are used, which theoretically
means twice the available frequencies
for a given number of channels.
One might wonder, with all these
advantages outstanding, why AM is used
much more than SSB in Citizens Band
radio today (not HAM or amateur
radio). The answer is quite simple; SSB
costs much more! SSB transceivers re-
quire several special circuits, called
balanced modulaton. and bandpass filters
for the transmitters. Beat frequency
oscillators (BFO) are also special circuits
required by SSB receivers.
Tne reason for the BFO is that there
is no carrier frequency to use as a
reference, therefore the BFO reinserts
one in the receiver. In receivers without
the BFO, the SSB signal is a garbled mess
of unintelligible sounds. These added
circuits are very expensive, hard to
tune, and very elaborate in design.
Specifically, the advantages of AM
are: with AM, it is easy to tune the
receiver and the transmitter; the design
is simple; and, most important, the
cost is nominal.
Is SSB worth the added cost and
trouble? It must be, or 95 percent of
the amateur radio operators (HAM-
not to be confused with Citizens Band
operators) around the world wouldn't
be using SSB today, and Allied Radio
Shack wouldn't be in the process of
designing one.
Tech note
As was stated last month in the
Tech Talk article, "FCC-an unrecog-
nized champion," FCC regulations place
5 watts as the maximum input power;
use of a linear Radio Frequency (RF)
amplifier is illegal.
To protect the license of the techni-
cian who works on Citizens Band equip-
ment, the technician should require
proof of a currently valid amateur radio
operator's license and a signed state-
ment certifying that the linear RF
amplifier will not be used on 11-meter
Citizens Band frequencies, before ac-
cepting the linear RF amplifier for
service.INTERCOM for August, 1971 15
-
o/ \
INT ER COM for August, 1971
1 5
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Tandy Corporation. Radio Shack Division. Intercom, Volume 5, Number 1, August 1971, periodical, August 1971; Fort Worth, Texas. (https://texashistory.unt.edu/ark:/67531/metadc1764309/m1/15/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Special Collections.