Circuit Description - Kenwood TK-90 Service Manual

Frequency Composition
This transceiver operates with double conversion fre-
quency composition.
ANT
RX MIX
LO1
TX MIX
Reference Signal Generator
TCXO is used for the reference frequency, fstd, which
controls the PLL, and is oscillating 15.6MHz. This reference
signal goes through the buffer amplifier (Q709) and is
doubled (to 31.2MHz) by the frequency multiplier (Q711).
This doubled signal is used as DDS (IC701) for a reference
signal of PLL from the first local oscillator and as the refer-
ence signal of DDS for CARs (IC702).
The doubled signal is further doubled with Q708 and
Q704, and released from the second local oscillator (LO2:
62.4MHz).
LO1
The output from the DDS (IC701) (8.340MHz~8.459MHz)
goes through ceramic filter CF701 and is input into the PLL IC
(IC703). The input signal is demultiplied by 8 (R) in the PLL IC
(IC703) and becomes the comparison frequency fø which is
1.041MHz~1.058MHz. VCO oscillates at 73.125MHz~
103.095MHz, and is input into the 6th pin of the PLL IC, and
then demultiplied to 1/N in the PLL IC. It is then compared
with the comparison frequency fø by the phase comparator
which locks the frequency and yields the LO1 output fre-
quency.

CIRCUIT DESCRIPTION /

73.095MHz
73.125~
103.095MHz
VCO2
VCO1
Q714
Q713
PLL
IC703
PLL REF
8.335~ DDS
8.468MHz IC701
CF1
Fig. 1 Frequency composition /
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TX/RX
MIX 10.695MHz
1st IF 2nd IF
LO2
TX
MIX
62.4MHz
Q708,704
x2
DDS REF DDS REF
31.2MHz
Q711
x2
fstd
X701
(TCXO)
15.6MHz
N
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AF OUT
CAR
MIC IN
CAR
10.695MHz
DDS
IC702
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