Circuit Description - Kenwood NXR-800 Service Manual Supplement

NXR-800
1. Transmitter main PLL circuit
The transmitter main PLL circuit consists of the VCO
(Q102 and Q103), PLL IC (IC101), IC102, Q104 and Q106
and produces the transmitter frequency signal.
The VCO Q102 produces transmitter frequencies
from 450.000MHz to 464.995MHz (K), 477.000MHz to
494.495MHz (K2).
The VCO Q103 produces transmitter frequencies
from 465.000MHz to 480.000MHz (K), 494.500MHz to
512.000MHz (K2).
The signal produced by the VCO (Q102 or Q103) is fed to
the buffer amplifi er and is amplifi ed by Q106. The higher
harmonic wave is attenuated by LPF and returns to the PLL
IC (IC101).
4.5MHz
TX DDS
circuit
6

CIRCUIT DESCRIPTION

IC102
OP-AMP
5V #2
IC101
PLL IC
9 4
1/R PD
Fref.=4.5MHz
R=45
1/N
Fpd=100kHz
6
Fig.1 Transmitter main PLL circuit
IC101 divides the VCO oscillating frequency signal and
transmitter PLL reference signal (4.5MHz), and compares
the phase with the 100kHz comparison frequency.
The phase difference signal produced by the comparing
phase is converted to a DC voltage by a lag-lead type loop
fi lter.
The DC signal is applied to varicaps D101, D102, D107,
and D108 to lock the VCO oscillator frequency with the de-
sired oscillator frequency.
At the same time, the DC signal passes through the
IC102 operational amplifier for monitoring the transmitter
main PLL lock voltage.
The output from the VCO passes through the buffer am-
plifi er Q104 and is supplied to the drive circuit.
9V'
CVT
450~
464.995MHz (K)
9V'
477~
D108
494.495MHz (K2)
Q102
465~
480MHz (K)
9V'
494.5~
D102
512MHz (K2)
Q103
ATT
450~
480MHz (K)
9V'
477~
512MHz (K2)
Q104
5V #2
ATT
Q106
Driver
circuit