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A portion of the AF signals from the AF amplifier (lC2) pass
through the low-pass filters (lC4alb) and are then amplified at
the tone amplifier (lC28a). The signals are applied to the
CTCSS decoder inside the CPU (1C20 pin 98) to control the
UAMUT" and "SP" ports.
When the DTCS system is in use, the amplified signals are
converted into digital signals at lC28b, then apptied to the
DTCS decoder inside the CPU (1C20 pin 23).
The "LFSW" port (1C20 pin 62) controls the LPF (lO4a)
characteristics to shift the cut-off frequency for CTCSS and
DTCS separately.
+2 TRANSMITTER CIRCUITS
4.2.1 MICROPHONE AMPLIFIER CIRCUIT
The microphone amplifier circuit amplifies the audio signals
with +6 dB/octave pre-emphasis characteristies from the
microphone to a level needed for the modulation circuit.
AF signals (MlC) from the FRONT unit via J5 (pin 't0) are
applied to the audio switch (1C25). While transmitting, the
MCON signalfrom the CPU is "High" and the AF signals pass
to the microphone amplifier circuit.
The AF signals from lC25 are applied to the microphone
amplifier lC (1C22) via the preamplifier (lC21b). The amptified
signals are applied to the limiter amplifier in 1C22,
The entered signals (1C22 pin 16) are pre-emphasized with
+6 dB/octave at a limiter amplifier, then passed throulh a
splutter filter. The output signals from pin 8 pass through the
level controller (lC5 pins 4, 3) and are then applied to the
modulation circuit (D23, D46) via Q52.
4-2.2 MODULATION CIRCUIT
The modulation circuit modulates the VCO oscillating signal
(RF signal) using the microphone AF signals.
o MICROPHONE
AMPLIFIER CIRCUIT
The AF signals from Q52 change the reactance of D23 and
D46 to modulate the oscillated signal at the Tx VCO circuit
(O23). The modulated signal is amptified at the buffer
amplifiers (Q19, Q20) and is then apptied to the drive amptifier
circuit.
The CTCSS/DTCS signals from lC5 (pin 2) are arnptified at
lC21a, and are applied to the reference oscillator circuit (e34,
X3, 014 for tC-F1010 0r X3; tC29 for tC-F1020) to modutate
the oscillated signal.
4.2-3 DRIVE/POWER AMPLIFIER CIRCUITS
The signal from the buffer amplifier (Q20) is passed through
the Tx/Rx switching circuit (D17), and amplified by the driver
(O15-Q17) and the power modute (tC1 1 ) to obtain 25 W
(lC-F1010) or 45 W (lC-F1020) of RF power.
The amplified signal is passed through the antenna switching
circuit (D4), low-pass filter and APC detector, and is then
applied to the antenna connector.
The collector voltages for drivers (Q15, Q16 for lC-F1010;
Q16 only for lC-F1020) come from the MTSV regutator (e38).
The transmit mute switch (Q39) controls the regulator when
transmit mute is necessary.
4-2-4 APC C|RCU|T
The APC circuit protects the power module (1C11) from a
mismatched output load and stabilizes the output power.
The APC detector circuit detects forward signals and reflection
signals at D3 and D1 respectively. The combined voltage is at
a minimum level when the antenna impedance is matched at
50 O and is increased when it is mismatched.
The detected voltage is applied to the inverse amplifier (lC10b
pin 5), and the power setting voltage (PSET) is apptied to the
other input (l C10b pi n 6) vi a the ampl i fi er ( t C10a) . When
antenna impedance is mismatched, the detected voltage
exceeds the power setting voltage. Then the output voltage of
the inverse amplifier (lC10b pin 7) controls the input current of
the power module (lC1 1) (and Q15 for lC-F j 020) to decrease
the output power.
. APC CIRCUIT
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