Kenwood TK-5210G Service Manual page 21

4-3. Transmit Signal Amplifi cation Circuit
(From T/R switch to Final amplifi er)
The transmit signal passing through the T/R switch (D101)
is amplifi ed to approx 100mW by the two transistor ampli-
fication circuits (Q101, Q102). The transmit signal output
from Q102 passes through a 3dB attenuator to improve
high-frequency signal matching is amplified by the drive
amplifier (Q103) and applied to the final amplifier (Q105).
The signal applied to the fi nal amplifi er is amplifi ed by the
fi nal amplifi er so that the antenna output is 5W (1W for Low
Power).
4-4. High-Frequency Signal Switch Circuit
(From Antenna switch to ANT output)
The transmit signal output from the fi nal amplifi er (Q105)
passes through the antenna switch (D106, D107) and
LPF, and goes into the SPDT switch (IC102, IC103) which
changes the antenna connector (CN101) and the universal
connector (CN102). The transmit signal passing through the
output change switch passes through the surge protection
HPF and spurious removing LPF and then goes to the an-
tenna connector (CN101) or the universal connector (CN102),
specifi ed by the SPDT switch (IC102, IC103).
Q101 Q102
Pre Pre Pre Drive
Drive AMP AMP
D101
T/R SW
5. PLL Frequency Synthesizer
5-1. VCXO (X301)
VCXO (X301) generates a reference frequency of
16.8MHz for the PLL frequency synthesizer. This reference
frequency is applied to pin 8 of the PLL IC (IC303).
The VCXO oscillation frequency is fi ne-adjusted by con-
trolling the voltage applied to pin 1 of the VCXO with DAC
(IC502). It is also controlled with pin 1 of the VCXO if the
output from VCXO is modulated.
5-2. VCO
There is a RX VCO and a TX VCO.
The TX VCO (Q311) generates a transmit carrier and
the RX VCO (Q310) generates a 1st local receive signal.
For the VCO oscillation frequency, the transmit carrier is
272 to 348MHz and the 1st local receive signal is 371.9 to
CIRCUIT DESCRIPTION
Q103 Q105
Drive Final
AMP AMP
3dB
Attenuator
Fig. 7 Transmitter circuit
4-5. APC circuit
The APC circuit detects the current of the drive ampli-
fier (Q103) and final amplifier (Q105) during transmission
and controls the output power by controlling the current. It
detects the current using R119 and R120 and applies a drop
voltage between both resistors during transmission to APC
IC (IC101). It controls the transmission current of the drive
amplifi er and fi nal amplifi er so that it is constant by compar-
ing this current with the reference voltage output from pin
7 of IC104. The reference voltage input to pin 5 of IC104 is
output from the DAC (IC502).
High/Low power output is set according to the DAC out-
put voltage.
4-6. Temperature Protection Circuit
The temperature protection circuit reduces the APC
voltage when the temperature of Q105 rises, to prevent
thermal destruction of the fi nal amplifi er (Q105). The ASIC
(IC10) detects the temperature with a thermistor (TH101) to
control the reference voltage to the APC circuit.
D106,D107
ANT SW
LPF
IC101
APC
APC SW
+B
447.9MHz.
The VCO oscillation frequency is determined by one sys-
tem of operation switching terminal "VCOSW1" and two
systems of voltage control terminals "CV" and "ASSIST".
The operation switching terminal, "VCOSW1", is controlled
by the ASIC (IC10). When the VCOSW1 logic is high, the RX
VCO outputs the signal. And if the logic is low, TX VCO out-
puts the signal.
The voltage control terminals, "CV" and "ASSIST", are
controlled by the PLL IC (IC303) and rheostat (IC414) and
the output frequency changes continuously according to the
applied voltage. For the modulation input terminal, "VCO_
MOD", the output frequency changes according to the
applied voltage. This is used to modulate the VCO output.
"VCO_MOD" works only when transmit is active (user
pressed PTT).
TK-5210
IC102
CN101
SPDT
CN102
IC103
SPDT
( G )
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