Circuit Description - Kenwood NXR-700 Service Manual

NXR-700
1. Transmitter main PLL circuit
The transmitter main PLL circuit consists of the VCO
(Q102 and Q103), PLL IC (IC101) and divide-by-2 circuit
(IC811) and produces the transmitter frequency signal.
The VCO Q102 produces transmitter frequencies
from 146.000MHz to 159.995MHz (K), 136.000MHz to
144.995MHz (K2). (The transmitter frequency of the VCO
is from 292.000MHz to 319.990MHz (K), 272.000MHz to
289.990MHz (K2).)
The VCO Q103 produces transmitter frequencies
from 160.000MHz to 174.000MHz (K), 145.000MHz to
154.000MHz (K2). (The transmitter frequency of the VCO
is from 320.000MHz to 348.000MHz (K), 290.000MHz to
308.000MHz (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).
4.5
MHz
9
TX DDS
circuit
6

CIRCUIT DESCRIPTION

9V'
IC102
OP-AMP
5V #2
IC101
PLL IC
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. The divide-by-2 circuit (IC811) divides the fre-
quency and produces the transmitter frequency. The output
level of IC811 is about +6dBm (4mW).
CVT
292~
9V' 9V'
319.99MHz (K)
272~
D108
289.99MHz (K2)
Q102 Q104
320~
348MHz (K)
9V'
290~
D102
308MHz (K2)
Q103
5V #2
ATT
Q106
292~ 146~
3V
174MHz (K)
348MHz (K)
272~ 136~
308MHz (K2) 154MHz (K2)
1/2
IC811
ATT
Driver
circuit