Kenwood TKR-740 Service Manual page 28

TKR-740
2.4 Transmitter main PLL circuit
The transmitter main PLL circuit produces the transmitter
frequency signal and consists of VCO (Q1 and Q2) and a single-
chip PLL IC (IC101). Transmit frequencies from 146.000 M Hz
t o 154.995 M Hz are derived f rom VCO Q1. Transm it
frequencies from 155.000 M Hz to 174.000 M Hz are derived
from VCO Q2.
IC101 divides the VCO oscillator signal and the transmitter
PLL reference signal (4.5 M Hz) and its phase is compared w ith
2.5 Driver circuit
The Driver circuit amplifies the transmitter frequency signal
to the level required for input to the final unit (X56-307 B/3).
This circuit consists of RF amplifier Q9, RF sw itch D7, RF
amplifier Q13, RF amplifier Q14, and sw itches Q203, Q8, Q12,
and Q11.
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CIRCUIT DESCRIPTION
the 100kHz comparison frequency. The phase difference signal
is converted to a DC signal w ith a lag-lead type loop filter. The
DC signal is applied to varicap D1, D3, D2, D4 to lock the VCO
oscillator frequency w ith the desired oscillator frequency. At
the same time, the DC signal passes through the IC109
operational amplifier and buffer amplifier, and is output as a
voltage signal (CVT) for monitoring the transmitter main PLL
lock voltage.
Fig.4 Transmitter main PLL circuit
milliw att). Since it is amplified by about 15 dB by Q13, and
also amplified by about 13 dB by Q14, the output from Q14
becomes about 630 milliw atts. After being attenuated by
attenuators R257, R258, and R259, the net output is +22 dBm
(160 milliw atts) at drive output connector CN1.
The transmitter signal level input to Q13 is about 0 dBm (1