Kenwood NXR-700 Service Manual page 9

5V #3
Internal
8
/External
5.99MHz
Ref circuit
IC407
or
10MHz
2-3. Transmitter modulation 19.2MHz PLL circuit
The transmitter modulation 19.2MHz PLL circuit produc-
es the reference frequency signal for the Transmitter DDS
circuit and modulates the low-frequency components.
The circuit consists of IC302, IC303, IC305, IC306, X301,
Q304, Q305, and Q307.
The signal generated by the VCXO (X301) is fed to the
buffer amplifi er Q307.
The VCXO (X301) signal enters buffer amplifier Q307
and is amplifi ed by Q305. The higher harmonic wave is at-
tenuated by the LPF and returns to IC303. Its phase is com-
pared with that of the reference frequency 5kHz.
The phase difference signal produced by the comparing
5V #2
TX Ref
19.2MHz
19.2MHz
PLL circuit
IC302
CIRCUIT DESCRIPTION
5V #3
IC401
OP-AMP
5V #3
IC404
PLL IC
2
1/R PD
X401
Fref.=19.2MHz
R=1920
6
1/N
Fpd=10kHz
Fig. 2 Transmitter reference 19.2MHz PLL circuit
IC306
OP-AMP
5V #2
IC303
PLL IC
8 2
1/R PD
Fref.=19.2MHz
R=3840
6
1/N
Fpd=5kHz
Fig. 3 Transmitter modulation 19.2MHz PLL circuit
CVT-REF
8V #2 8V #2 5V #1
19.2MHz
Q417 Q416
8V #2 5V #2
Q401
Q415
5V #2
Q402
phase is converted to a DC voltage by a lag-lead type loop
fi lter. This DC voltage is input to the IC305 invert amplifi er
(B/2) and is synthesized with the modulating signal. This DC
voltage is input to the X301 control voltage terminal for con-
trolling the VCXO oscillating frequency 19.2MHz.
The DC voltage passes through the IC306 operational
amplifi er, and is output as a voltage signal (CVT-MOD) for
monitoring the modulating 19.2MHz PLL circuit lock voltage.
The 19.2MHz oscillating signal is fed to the Q307 buffer
amplifier and is amplified by Q304. The higher harmonic
wave is attenuated by the LPF, fed to IC307, and is used as
the reference frequency signal of the transmitter DDS circuit.
5V #2
CVT-MOD
Mod signal
5V #2 8V #2
19.2MHz
IC305 X301
8V #2
Q305
NXR-700
5V #1
19.2MHz
Q412
CN406
19.2MHz
CN405
19.2MHz
8V #2 5V #2
19.2MHz
Q307 Q304
TX Mod
19.2MHz
PLL circuit
RX unit
TX DDS
circuit
9