RECEIVING SSB SIGNALS
There are four types of signals presently used for communications: FM,
AM, USB and LSB. When the MODE switch on your unit is placed in the
AM position, only standard double-sideband 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 AM or FM detector to procedure an
intelligible output. The USB and LSB modes will detect upper sideband and
lower sideband respectively and standard AM signals.
SSB reception differs from standard AM reception in that SSB receiver
does not require a carrier or opposite sideband to produce an intelligible
signal. A single-sideband transmitted signal consists only of the upper or
lower sideband 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 that make even moderately strong AM signals unreadable.
Also, SSB takes only half 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 sideband signals
(USB) may be made intelligible
only
if the receive is functioning in the USB
position.
If a lower sideband (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 modulation is applied to
the transmitter’s microphone in the USB mode, the transmitter’s output
frequency is increased whereas in the USB 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 single tone of modulation will result, and if the tone is
increased in frequency (such as a low-pitched whistle 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 voice lock control. When listening to an AM transmission, a correct
sideband is heard in either mode since both upper and lower sidebands are
received.
Once the desired SSB mode has been selected, frequency adjustment
may be necessary in order to make the incoming signal intelligible, the
CLARIFIER control allows the operator to vary frequency above and below
the exact-center frequency of the received signal. If the sound of the
incoming signal is high or low pitched, adjust the operation of the
CLARIFIER. Consider it as performing the same function as a phonograph
speed control. When the speed is set to high, voices will be high-pitched and
if set too low, voices will be low-pitched. Also, there is only one correct
speed that will make a particular record procedure the same sound that was
recorded. If the record is played on a turntable that rotated in the wrong
direction (opposite sideband) no amount of speed control (CLARIFIER) 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 tuned to exactly the same frequency by the CLARIFIER control. For
simplicity it is recommended that the AM modes be used to listen to AM
signals.
ROGER BEEP
When your transceiver is on normal operation, your radio automatically
transmits the audio sign at the end of your transmission. The listener can note
easily that your transmission is over through the sign. Please note that this
ROGER BEEP transmits 0.15-second at the moment PRESS-TO-TALK
SWITCH KNOB is off.
Fig. 2.
- 13 -
- 14 -
