Icom IC-720 Instruction Manual page 15

The display will automatically select USB when зет то
10МН2 and above, and LSB 9MHz and below. If reverse
SSB is desired push the Function button then push the SSB
button.
5-2 SSB OPERATION
5-2-1 RECEIVING
After connecting an antenna, microphone, etc, set the
knobs and switches as follows:
Before turning the set on, be sure that the Ham Band/
General Coverage is in the Ham Band position (out),
Transmit-Receive is in Receive (out), VOX off (out) ATT
off (out), AGC slow (out), Noise Blanker (NB) off (out),
AF Gain Control completely counterclockwise, RF Gain
Control completely clockwise, Pass Band Tuning (PBT) is
turned completely counterclockwise to off (a click will be
heard), Receiver Incremental Tuning (RIT) button off (out).
Other controls are not related to receiving, disregard them
for this period.
Turn on the Power Switch, the display will read
(іа 718000] next, push the Band Up or Down
Button to select the frequency you wish то listen to, turn
the AF Gain Control slowly clockwise until a comfortable
listening level is reached. Rotate the Tuning Knob until a
signal is received. The Meter will indicate the signal strength,
for more accurate tuning push the Dial Select button in for
10Hz and tune to the highest meter reading. If the signal
you have selected is on the opposite sideband and you can-
not receive it clearly push the Function button and then
the SSB button, reversing the sideband. With the Dial
Select but on (in) the tuning change is 10Hz, therefore the
maximum possible difference in your reception and the
signal's frequency is 5Hz. This difference is negligible and
indeed, may be difficult to detect. This system, as opposed
to continuously variable frequency systems provides more
accurate and convenient tuning.
5-2-2 NB (Noise Blanker)
Push the Noise Blanker button in when there is pulse-type
noise present, such as ignition noise from automobile
generators or alternators, etc, Noise will be suppressed, and
weak signals heard more clearly. The Noise Blanker is less
effective against strong signals on a nearby frequency, or
continuous (not pulse) noise.
5-2-3 AGC (Automatic Gain Control)
The ІС-720 has а "Напа" AGC system which holds the peak
voltage of rectified AF signals from the detector circuit for
a predetermined period. During normal puases in speech
noise will not be heard. The Multi-Function Meter also will
"hang" for a period to facilitate "S" readings.
—13—
When signals are received that have short interval fading
push the AGC button in for FAST. This will turn the hang
AGC circuit off, and the time constant will be shortened.
Always use the Fast position for RTTY.
5-2-4 ATT (ATTENUATOR)
When strong nearby signals make "5" reading difficult, or
reception poor, push the ATT button. Doing so inserts a
20dB attenuator into the receiving antenna circuit. This
serves to provide more stable receiption and reduce inter-
fering signals. Normally the button should be left in the
off position (out).
5-2-5 P.B. (PASS BAND) TUNING
Pass Band Tuning is a system in the receive mode to narrow
the band width (selectivity) of the frequencies that will pass
through the crystal filter electrically from either the upper
or lower side continuously by up to .7KHz. This is very
effective in reducing interference from nearby signals.
To use the PBT system, rotate the PBT control clockwise
¿until it clicks оп and continue rotating it to its mid range
position. This is the widest position and is equivalent to
the bandwidth in the off position.
For example, while receiving in the LSB mode, if you get
interference from a lower frequency (interfering signals are
high pitched tones), narrow the band width by turning the
P.B. tuning control counter-clockwise. When the interfer-
ing signals are low pitched tones, they are from a higher
frequency, and you should narrow the band width by
turning the P.B. tuning contro! clockwise.
When receiving in the USB mode, the band width is nar-
rowed in the opposite manner. Interference from а higher
frequency will be high pitched tones, and the P.B. tuning
control should be turned clockwise. Interference from а
lower frequency will be low pitched tones and the P.B.
tuning control is turned counter clockwise.
When Р.В. TUNE knob is turned
counter-clockwise
Receiving LSB signa!
BFO frequency Pass band 15 narrowed
and mterfering signal
goes out of the pass band
Receiwin 4 signat
Interference
Interfering signal
When Р.В TUNE knob 15 turned
clockwise
Receiving LSB signai
Pass band 15 narrowed
and interfering signat
goes out of the pass band
interfering signal
BFO frequency
Interference
Recerving signat