4 - 5
ATT
ANT
SW
PWR
DET
PWR
AM P
LPF
LPF
APC
CTRL
YGR
AM P
DRIVE
AM P
LPF
GATE
CTRL
HP F
TX/RX
SW
PWR
DET
ANT
SW
LO
AMP
BPF
D101,102
IC150B
PSET
D59,60
Q100
Q102
D50,53
Q101
IC100
D 100,850
IC150A
Q152
L1-3
C1-6
L100.101.153
C100-103,192
L102,103
C106,107
L5-7
C10-14
L4,C7-9
ANT
Q153
D154-156
D150,152,153
DSET
VHF TX signal
UHF TX signal
FILTER
LOOP
VCO
BUFF
BUFF
TX/RX
SW
PLL
IC
VCO
LO
AMP
VCO
LPF
RF UNIT
Q201
D850
IC800
UHF BAND:
319.175-538.345 MHz
VCO UNIT
Q101,102,D100-104
Q1,2,D1-3,5,6
Q51,52,D51-55
Q200
BC BAND: 62.145−131.645 MHz
Q202
1st LO signals
(A BAND)
D 100
VHF BAND:
131.350-235.645 MHz
15.3MHz reference frequency
Modulation signals
APC CIRCUIT (RF UNIT)
The APC (Automatic Power Control) circuit stabilizes
transmit output power to prevent transmit output power level
change which is caused by load mismatching or heat effect,
etc.
TX signal is passed through the power detector (VHF; D59,
60/UHF; D50, 53). The power detector rectifies a portion
of the TX signal and converts it into DC voltage which is in
proportion to the transmit output power. The detected voltage
is applied to the APC controller (IC150B). The TX power
setting voltage “PSET” is applied to another input terminal as
the reference voltage.
The output voltage is applied to the ATT (D101, 102) to con-
trol the attenuation level, to adjust the input level of the YGR
AMP (Q102) so that the TX output power is stable.
The setting of TX power is carried out by applying voltage
“PSET” to the APC controller (IC150B). The output voltage of
the controller controls the bias of the drive and power AMPs
to reduce/increase the gain of these amplifi ers to set the TX
output power to High, Mid., Low and S-Low.
4-3 FREQUENCY SYNTHESIZER CIRCUITS
VCOs
This transceiver has total of five VCOs; one RX VCO and
RX/TX VCOs on the VCO UNIT, and two RX VCOs on the
MAIN UNIT.
• BC BAND VCO (VCO UNIT; Q1, D1, 3, 5, 6
)
The BC BAND VCO generates the 1st LO for BC band
(0.495–75.995 MHz) RX.
• VHF BAND VCO (VCO UNIT; Q51, D51, 54)
The VHF BAND VCO generates the 1st LO for VHF band
(76–173.995 MHz) RX, and also TX signal for the operation
on the VHF band.
• UHF BAND VCO (VCO UNIT; Q101, D101–104)
The UHF BAND VCO generates the LO for UHF band (174–
599.995 MHz) RX, and also TX signal for the operation on
the UHF band.
When receiving 600 MHz and higher signals, the UHF BAND
VCO oscillates 269.175–469.17 MHz 1st LO signals, and the
output signal is doubled by the doubler (MAIN UNIT; Q850,
D851) before being applied to the mixer (MAIN UNIT; IC900).
PLL (VCO AND MAIN UNITS)
The PLL circuit provides stable oscillation for both of the
transmit and 1st LO frequencies. By comparing the fedback
VCO output and the reference frequency signal, the oscillating
frequency is stabilized. The PLL output frequency is controlled
by the serial data including divide ratio from the CPU.
A portion of output signals from each VCO are fedback
to the PLL IC (MAIN UNIT: IC800) via buffers (VCO:
Q200, 202) and LPF. The applied VCO outputs are divided
by the prescaler and programmable divider, then phase-
compared with divided reference frequency from X450
(MAIN). The phase difference is output via the charge pump,
and applied to the VCOs as lock voltage via the loop filter.
When the oscillation frequency drifts, its phase changes
from that of the reference frequency, causing a lock voltage
change to compensate for the drift in the VCO oscillating
frequency.
• TX AMPLIFIERS AND APC CIRCUIT
• FREQUENCY SYNTHESIZER CIRCUITS
