Kenwood NXR-800 Service Manual Supplement

NXR-800
6
CIRCUIT DESCRIPTION
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).
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.
Q106
TX DDS
circuit
1/R
1/N
PD
Fref.=4.5MHz
R=45
Fpd=100kHz
5V #2
Q104Q102
9V’ 9V’
9V’
5V #2
450~
464.995MHz (K)
477~
494.495MHz (K2)
450~
480MHz (K)
477~
512MHz (K2)
IC102
OP-AMP
49
6
4.5MHz
IC101
PLL IC
CVT
Driver
circuit
D108
D107D101
Q103
9V’
465~
480MHz (K)
494.5~
512MHz (K2)
D102
ATT
ATT
Fig.1 Transmitter main PLL circuit

Kenwood NXR-800 Specifications

General

Brand	Kenwood
Model	NXR-800
Category	Repeater
Language	English