TK-90
19
Frequency Composition
This transceiver operates with double conversion fre-
quency composition.
CIRCUIT DESCRIPTION /
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PLL
IC703
VCO1
Q713
VCO2
Q714
73.125~
103.095MHz
CF1
PLL REF
8.335~
8.468MHz
DDS
IC701
DDS
IC702
DDS REF
DDS REF
73.095MHz
1st IF
10.695MHz
2nd IF
LO1
RX MIX
TX MIX
TX/RX
MIX
LO2
62.4MHz
Q708,704
x2
Q711
x2
RX MIX
TX
MIX
31.2MHz
fstd
X701
(TCXO)
15.6MHz
10.695MHz
CAR
CAR
AF OUT
MIC IN
ANT
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.
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Fig. 1
Frequency composition /
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