RECEIVING SSB SIGNALS
There are four types of signals presently used for communications in the Citizens
Band : FM, AM, USB and LSB. When the MODE switch on your unit is placed in the
AM position, only standard double-side band and in FM position, only frequency
deviation, full carrier signals will be detected. An SSB signal may be recognized while
in the AM or FM mode by its characteristic "Donald Duck" sound and the inability of
the detector to produce an intelligible output. The USB and LSB modes will detect
upper side band and lower side band respectively, and standard AM signals.
SSB reception differs from standard AM reception in that an SSB receiver does not
require a carrier or opposite side band to produce an intelligible signal. A single-side
band transmitted signal consists only of the upper or the lower side band and no carrier
is transmitted. The elimination of the carrier from the AM signal helps to eliminate the
biggest cause of whistles and tones heard on channels which make even moderately
strong AM signals unreadable. Also, SSB takes only half the space of an AM channel,
therefore two SSB conversations will fit into each channel, expanding the 40 AM
channels to 80 SSB channels. The reduction in channel space required also helps in the
receiver because only half of the noise and interference can be received with 100% of
the SSB signal.
An SSB signal may be received only when the listening receiver is functioning in the
same mode. In other words, an upper side band signal (USB) may be made intelligible
only if the receiver is functioning in the USB position.
If a lower side band (LSB) signal is heard when the receiver is in the USB mode, no
amount of tuning will make the signal intelligible. The reason for this may be
understood if you consider that when the modulation is applied to the transmitter's
microphone in the USB mode, the transmitter output frequency is increased whereas in
the LSB mode the transmitter's output frequency is decreased.
The result in listening to the receiver is that when the MODE switch is in the proper
position (either USB or LSB), a true reproduction of a single tone of modulation will
result, and if the tone is increased in frequency (such as a low-pitched whistle or a high-
pitched whistle) you will hear the increase in the output tone of the receiver. If the
incorrect mode is selected, an increase in tone of a whistle applied to the transmitter
will cause a decrease in the resultant tone from the receiver.
Thus when a voice is used in place of a whistle or tone, in the proper listening mode
the voice will be received correctly whereas in the incorrect mode, the voice will be
translated backwards and cannot be made intelligible by the FINE/COARSE control.
When listening to an AM transmission, a correct side band is heard in either mode since
both upper and lower side bands are received.
Once the desired SSB mode has been selected, frequency adjustment may be
necessary in order to make the incoming signal intelligible. The FINE/COARSE control
allows the operator to vary frequency above or below the exact frequency of the
channel. If the sound of the incoming signal is high or low pitched, adjust the operation
of the FINE/COARSE.
Consider it as performing the same function as a phonograph speed control. When the
speed is set too high, voices will be high-pitched and if set too low, voice will be low-
pitched. Also, there is only one correct speed that will make a particular record produce
the same sound that was recorded. If the record is played on a turntable that is rotated in
the wrong direction (opposite side band) no amount of speed control (FINE/COARSE)
will produce an intelligible sound.
An AM signal received while listening in one of the SSB modes will produce a steady
tone (carrier) in addition to the intelligence, unless the SSB receiver is tuned to exactly
the same frequency by the FINE/COARSE control. For simplicity, it is recommended
that the AM modes be used to listen to AM signals.
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