Icom IC-720A Instruction Manual page 19

you тау Бе receiving in the opposite sideband. ІҒ5о, change
the mode to the proper sideband, by pushing the FUN-
CTION switch, then SSB switch.
5-2-2 NB (NOISE BLANKER)
Turn the noise blanker ON (in) when there is pulse type
noise, such as ignition noise from automobile motors. Noise
will be suppressed and even weak signals will be received
comfortably. The noise blanker will effectively work for
"woodpecker's noise", however, if the receiving signal is
too strong, the noise blanker may work with the receiving
signal itself, and some distortion may cause in the receiving
audio or keying form. At this time, turn the noise blanker
OFF.
5-2-3 AGC (AUTOMATIC GAIN CONTROL)
The 1С-720А has a fast attack/slow release AGC system
which holds the peak voltage of rectified IF signals from the
(Е amp circuit for а certain period. Therefore, during the
pauses in normal speech of the received signal, uncomforta-
bie noise will not be heard. The meter indicates the peak
value for a certain period, facilitating reading of the meter
"S" function.
For normal SSB reception, set the AGC switch in the OUT
(slow) position. Set the AGC Switch in the FAST (IN)
position, when tuning or receiving signals with short interval
fading. When in the FAST position, the time constant is
shortened.
5-2-4 ATT (ATTENUATOR) SWITCH
Turn the ATT switch ON (IN) when strong nearby signals
disturb signal reception or make "5" reading difficult. In
the ON position, the RF amplifier is removed from the
circuit and a 10dB attenuator is inserted into the receiving
antenna circuit, reducing interfering signals and giving more
stable reception. In normal operation the ATT switch is
left in the OFF (OUT) position.
5-2-5 Р.В. (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 800Hz. This is very
effective in reducing interference from nearby signals.
To use the PBT system, rotate the PBT control clockwise
until it clicks on 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 counterclockwise. 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 control clockwise.
When receiving in the USB mode, the band width is nar-
—16—
rowed іп 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 a
lower frequency will be low-pitched tones and the P.B.
tuning control is turned counterclockwise.
When Р.В. TUNE knob is turned
counter-clockwise.
Receiving LSB signal
BFO frequency Pass band is narrowed
and interfering signal
goes out of the pass band.
Receiving попа!
Interference
Interfering signal
When Р.В. TUNE knob 15 turned.
clockwise.
Receiving LSB signal
Pass band is narrowed
and interfering signal
goes out of the pass band.
Interfering signal
BFO frequency
Interference
Receiving signal
This control can also be used for audio tone adjustment, so
it may be set for the most comfortable reception.
5-2-6 TRANSMITTING
Before transmitting, listen in the receive mode to make sure
your transmission will not interfere with other communi-
cations. ІТ possible, use a dummy load for adjustment
instead of an antenna. Set knobs and switches as follows.
MIC GAIN CENTER
RF POWER CONTROL OFF (clockwise til it '"clicks'')
METER SELECT SWITCH ALC
Other knobs and switches are left in the same positions as
for receiving. When the T/R switch is moved to transmit,
or when the PTT (push-to-talk) switch on the microphone
is depressed, the TRANSMIT Indicator is illuminated. By
speaking into the microphone, the meter needle will move
according to the strength of your voice and SSB signals will
be transmitted. Set the MIC GAIN control so that the
meter needle stays well within the blue ALC zone at voice
peaks. Change to the receive mode by moving the T/R
switch to receive, or release the microphone PTT switch.
5-2-7 HOW TO USE THE SPEECH PROCESSOR
The Pass-Band Tuning system acts as a low distortion RF
Speech Processor. This enables greater talk power and
better results in DX operation. Follow the steps below for
use of the RF Speech Processor:
Set to the CENTER
(12 o'clock) position.
MIC GAIN CONTROL