Icom i703, Руководство по обслуживанию

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3 - 4
3-1-13 AF SELECTOR SWITCH (MAIN UNIT)
The AF signals from one of the detector circuits are applied
to the AF selector switch (IC2301). IC2301 consists of dual
3-channel analog switches which are selected with a mode
signal and the squelch control signal.
3-1-14 AF AMPLIFIER CIRCUIT (MAIN UNIT)
The AF amplifier amplifies the demodulated signal to a suit-
able driving level for the speaker.
The AF signals from the AF selector switch (MAIN unit;
IC2301) pass through the 3 kHz low-pass filter (IC2401),
and are then applied to the DSP switch (IC2461, pin 6)
which mute the beep sound when DSP unit’s power ON or
OFF.
The AF signals are applied to the VCA (Voltage Controlled
Amplifier) circuit (IC7201). The AF gain setting from the main
CPU is converted to DC voltage at the D/A converter
(IC6501) and applied to the VCA control terminal (IC7201)
via the “AFGV” signal line.
The CW side tone/beep tone (“BEEP” signal from the buffer
amplifier IC7001, pin 8) and optional synthesized voice
(“SPCH” signal from the UT102) are also applied to the VCA
circuit.
The output AF signals from IC7201 (pin 9) are power-ampli-
fied at IC7301 to drive the speaker, and are then applied to
the speaker (CHASSIS unit; SP1) via J7372.
3-2 TRANSMITTER CIRCUITS
3-2-1 MICROPHONE AMPLIFIER CIRCUIT
(MAIN UNIT)
The microphone amplifier circuit amplifies microphone input
signals and outputs the amplified signals to the balanced
modulator or FM modulation circuit.
Audio signals from the front or rear panel [MIC] connector
enter the microphone amplifier IC (IC1621, pin 12) and are
then amplified at the microphone amplifier or speech com-
pressor section via the R1621.
The amplified or compressed signals are applied to the VCA
section of IC1601. The microphone gain setting from the D/A
converter (IC6501, pin 11) is applied to the VCA control ter-
minal (IC1601, pin 8). The resulting signals from pin 9 are
then applied to the buffer amplifier (Q1721) via the analog
switch (IC1701). External modulation input from the [ACC]
socket (J6951, pin 11) is also applied to Q1721.
While in SSB mode, the amplified signals from the buffer
amplifier (Q1721) are passed through the AF selector switch
(IC1751) and are then applied to the balanced modulator
(IC1801).
While in AM/FM mode, the amplified signals from the buffer
amplifier (Q1721) are applied to the IDC amplifier (IC2201).
The signals are then applied to the AF selector switch
(IC1751) via the AM depth controller (R2618) in AM mode or
to the varactor diode (D9622) via the FM max deviation con-
troller (R2621) and AF selector switch (IC2651) in FM mode.
3-2-2 VOX CIRCUIT (MAIN UNIT)
The VOX (Voice-Operated-Transmission) circuit sets trans-
mitting conditions according to voice input.
When the VOX function is activated, the microphone signals
are amplified at microphone amplifier (IC1621, pin 10), and
are then applied to the VOX comparator section in the main
CPU (IC5901, pin 93) via the “VOXL” line.
A portion of the power amplified AF signals from the AF
power amplifier (IC7301) are amplified at the buffer amplifi-
er (IC7001, pin 13) and applied to the anti-VOX comparator
section in the main CPU (IC5901, pin 92) via the “AVXL”
line.
Then the main CPU compares these and controls the trans-
mitter circuit.
3-2-3 BALANCED MODULATOR (MAIN UNIT)
The balanced modulator converts the AF signals from the
microphone amplifier to a 9 MHz IF signal with a BFO (Beat
Frequency Oscillator) signal.
Microphone signals from the AF selector switch (IC1751) are
applied to the balanced modulator (IC1801, pin 3). The BFO
signal is applied to IC1801 (pin 1) as a carrier signal.
13
INH
15
12
9, 10
14
X2
X0
X
X1
SSB/CW/
RTTY
IC2301
FM
AM
6
AFS1, AFS2
SQL
AF signal
to the AF amplifie
AF signals from
the microphone
"VOXL" signal
IC1621
IC1602
"VOXL" signal
"COMS" signal
IC1601 IC1701
to the modulation circuit
Amp.
Comp.
VCA
12
10
14
7
8
Amp.
SW
• AF SELECTOR SWITCH
• MICROPHONE AMPLIFIER CIRCUIT