Icom IC-F4060, Service Manual

Page: 167 / 203

5 - 3
Power
amp.
ALC
amp.
Drive
amp.
+
–
HV
• APC CIRCUIT
to the anntena
“T2”
“TMUT”
from buffer amplifier (Q7)
T5V
Q602
Pre-
drive
amp.
Q603
IC601
Q601
to the receive circuits
LPF
LPF
ANT
SW
D604
Power detecter
D607
Q606
The output AF signals are then passed through the Digital/
Analog switch (IC14, pins 12, 14) and applied to the AF mixer
(IC9, pin 6) where the MIC signals and Tone signals are mixed
with (while CTCSS/DTCS are in use) via the PM/FM switch
(IC13, pins 12, 14).
The CTCSS and DTCS signals are generated by the CPU
(IC18) and output from pins 89−91. The output signals are
passed through the 3 registers (R263–R265) to change its wave
form. The wave form changed CTCSS/DTCS signals are passed
through the LPF (IC17, pins 1, 3) and the D/A converter (IC4,
pins 21, 22) for level adjustment. The level adjusted CTCSS/
DTCS signals are then applied to the AF mixer (IC9, pin 6).
2/5 tone and DTMF signals are generated by the CPU (IC18)
and output from pin 43. The output signals are passed through
two LPF’s (IC17, pins 8, 10 and pins 5, 7), then applied to the AF
mixer (IC9, pin 6).
The mixed AF signals are output from pin 7 of the AF mixer
(IC9) and passed through the D/A converter (IC4, pins 3, 4) for
level adjustment (=deviation adjustment), then applied to the
modulation circuit (D11) as the modulation signals.
The modulation signals are also applied to the reference
frequency oscillator (X1) via D/A converter (IC4, pins 11, 12)
and AF amplifi er (IC21, pins 1, 4).
5-2-2 MODULATION CIRCUIT (MAIN UNIT)
The modulation signals from the microphone amplifi er circuits
are applied to the D11, and modulate the VCO oscillating
signal by changing the reactance of D11. The modulated VCO
output signal is buffer-amplifi ed by Q4 and Q6, then applied to
transmit amplifi ers as a transmit signal via the TX/RX switch
(D14 is ON, D15 is OFF) and buffer amplifi er (Q7).
5-2-3 TRANSMIT AMPLIFIERS (RF UNIT)
The transmit signal from the buffer amplifi er (MAIN UNIT; Q7)
is amplifi ed to the transmit output level by pre-driver (Q603),
driver (Q602) and power (Q601) amplifi ers.
The power-amplifi ed transmit signal is passed through the two
staged LPF (L607, L608, C612, C616, C620, C623, C624) to
fi lter off the harmonic components in the transmit signal. The
fi ltered transmit signal is passed through the antenna switching
circuit (D601, D602 and D603 are ON), then applied to the
antenna connector (CHASSIS; J1) via another LPF (L601−
L603, C601−C607).
5-2-4 APC CIRCUIT (RF UNIT)
The APC (Automatic Power Control) circuit stabilizes transmit
output power to prevent the transition of the transmit output
power level which is caused by load mismatching or heat
effect, etc. The APC circuit also selects transmit output power
from high, middle and low power.
A portion of the transmit signal is detected by the transmit power
detector (D604, D607) to produce a DC voltage corresponding to
the transmit output power level. The detected voltage is applied
to the APC amplifier (IC601, pin 3). The transmit power setting
voltage “T2” from the D/A converter (MAIN UNIT; IC20, pin 2) is
applied to another input terminal (pin 1) as the reference voltage.
The APC amplifi er compares the detected voltage and reference
voltage, and the difference of the voltage is output from pin 4.
The output voltage controls the bias of the pre-drive (Q603),
drive (Q602) and power (Q601) amplifiers to reduce/increase
the gain of these amplifi ers for stable transmit output power.
The change of transmit output power is carried out by the
change of reference voltage “T2,” and the transmit power
muting is carried out by the TX mute switch (Q606), using the
“TMUT” signal from the CPU (IC18, pin 13).
5-3 PLL CIRCUITS
5-5-1 VCO (Voltage Controlled Oscillator) CIRCUITS
(MAIN UNIT)
A VCO is a oscillator which its oscillating frequency is
controlled by adding voltage (lock voltage).
This transceiver has 3 VCO’s; RX VCO1 (Q1, D1, D2), RX
VCO2 (Q2, D5, D6) and TX VCO (Q3, D9, D10). The RX VCO1
oscillates the 1st LO signals for 435 MHz/485 MHz ( (Low band/
High band) and higher, and the RX VCO2 oscillates the 1st LO
signals for 435 MHz/485 MHz ( (Low band/High band) and lower
frequencies. And the TX VCO oscillates the transmit output
signal.
• RX VCO1 and RX VCO2
The RX VCO1/RX VCO2 (Q1, D1, D2/Q2, D5, D6) oscillates
the 1st LO signals. The output signals are amplified by the
buffer amplifi ers (Q4, Q6), and applied to the 1st mixer (Q37)
via TX/RX switch (D14 is OFF, D15 is ON) and LPF (L38,
C160, C161), to be mixed with the received signals to produce
the 46.35 MHz 1st IF signal.
• TX VCO
The TX VCO (Q3, D9, D10) oscillates the transmit signal. The
output signal is applied to the transmit amplifi ers via the buffer
amplifi ers (Q4, Q6) and TX/RX switch (D14 is ON, D15 is OFF).
A portion of the each VCO output is applied to the PLL IC (IC1,
pin 6) via the buffer amplifi ers (Q4, Q5) and the tunable BPF
(D16, D17, L40, C151, C152, C154).
5-5-2 PLL CIRCUIT (MAIN UNIT)
The PLL circuit provides stable oscillation of the transmit frequency
and receive 1st LO frequency. The PLL output frequency is
controlled by the divided ratio (N-data) from the CPU.