Icom IC-720A Instruction Manual page 10

1. MULTI-FUNCTION METER
When in the receive mode the meter acts as an S meter
regardless of the position of the meter select switch. Signal
strength is indicated оп a scale of 51-59, and 59+204В то
59+4 048.
In the transmit mode Ше meter has three functions which
are selected by the Meter Select Switch (31) and the IC
Meter Switch inside the top dtcess cover. They are as
follows:
іс; Indicates the collector current of the final transistors.
Po; Indicates the relative output power. SWR can be
measured by placing the switch located inside the top cover
to the SWR position.
ALC; In this position the meter functions when the RF
output reaches a certain level.
2. RF POWER CONTROL
The IC-720A has a built-in RF speech processor which is
turned ON by turning the control counterclockwise, from
the COMP OFF position. (a click will be heard.) іп the
ON position. it functions as the RF drive control, as ex-
plained in the MIC GAIN CONTROL paragraph. In CW,
SSB and RTTY modes it operates as the output level control
of the IC-720A. When this function is not desired the
control should be turned completely clockwise until COMP
OFF, and a click is heard.
3. MIC GAIN CONTROL
Adjusts the level of modulation according to the input of
the microphone. Clockwise rotation increases the micro-
phones gain. As the input will vary with different micro-
phones and different voices, the knob should be turned until
the Multi-Function Meter needle, in the ALC mode, begins
to move slightly within the ALC zone. In SSB and AM
modes, when the RF speech processor is in use, the MIC
GAIN CONTROL sets the clipping limits, while the RF
POWER CONTROL sets the RF drive level to the maximum
power level, where ALC starts at the saturation point of the
amplifiers.
4. POWER SWITCH
The POWER SWITCH is a push-lock type switch which
controls the input DC power to the IC-720A. When the
external AC power supply (!С-Р515) is used, the switch also
acts as the AC power supply switch. When the switch is
pushed in and locked, power is supplied to the set. When
the switch is pushed again and released, power is cut to all
circuits except the PA unit. (When the BC-10A is used,
power will also be supplied to the CPU.)
5. PHONES JACK
Accepts a standard 1/4 inch headphone plug for headphones
of 4 ~ 16 ohms. Stereo phones can be used without modi-
fication.
6. MIC CONNECTOR
Connect the supplied microphone or optional microphone
ay ee
(С-5М5 to this jack. If you wish to use a different micro-
phone, refer to the drawing on page 4.
7. АЕ GAIN CONTROL
Controls the audio output level in the receive mode. Clock-
wise rotation increases the level.
8. RF GAIN CONTROL
Controls the gain of the RF section in the receive mode.
Clockwise rotation gives the maximum gain. As the control
is rotated counterclockwise, the needle of the MULTI-
FUNCTION METER rises, and only signals stronger than
the level indicated by the needle will be heard.
9. TRANSMIT/RECEIVE (T/R) SWITCH
This switch is for manually switching from transmit to
receive and vice versa. Set the switch to RECEIVE (out)
and the 1С-720А is in the receive mode. Set the switch to
TRANSMIT (in) and it switches to transmit. When switch-
ing with the PTT switch on the microphone or with the
VOX switch set to ON, the T/R switch must be in the
RECEIVE position.
10. VOX SWITCH
This switches the VOX circuit ON and OFF. When it is in
the ON (in) position, in SSB or AM, T/R switching is
accomplished by means of a voice signal. In CW operation,
semi-break-in switching by means of keying is possible.
11. TUNING RATE SELECT SWITCH
The small vernier marks on the tuning knob are changed to
correspond to 10Hz steps or 100Н2 steps which is selected
by this switch.
12. Р.В. TUNE (PASS BAND TUNING) CONTROL
Allows continuous tuning of the pass-band selectivity by
moving the filter up to 800Hz from the upper or lower side
in SSB, CW and RTTY. Not only improves selectivity, but
also can improve the audio tone. Normal position is in the
center (12 o'clock) position and is 2.3K Hz wide in SSB.
13. RIT CONTROL
Shifts the receive frequency +800Hz either side of the trans-
mit frequency. When the RIT is ON, the RIT INDICATOR
is illuminated. Rotating the control to the (+) side raises
the receiver frequency, and rotating to the (—) side lowers
the receiver frequency. With the RIT ON, if the TUNING
CONTROL KNOB is moved one increment, the RIT circuit
is automatically pulsed OFF. Therefore it is unnecessary to
manually turn OFF the RIT when changing operating fre-
quency. The frequency shift by tuning the RIT Control is
not indicated on the frequency display.
14. TUNING SPEED BUTTON
Pushing the TUNING SPEED BUTTON will illuminate the
DIAL TS INDICATOR, and the small vernier marks on the
tuning knob are changed to correspond to 1KHz steps. At
the same time, the 100Hz digit is turned OFF on the display.
When the TUNING SPEED BUTTON is depressed again,
the DIAL TS INDICATOR goes OFF and the small vernier
marks will again correspond to 100Hz steps or 10Hz steps.