Kenwood TS-120S Service Manual

FUNCTIONAL DESCRIPTION
TS-120S FREQUENCY SYSTEM
The TS-120S employs single conversion with a unique PLL
circuit, as shown in Fig. 1.
The frequency system is basically that of the TS-820 with the
exception of the PLL circuit.
PLL CIRCUIT
VCO output is obtained by synthesizing the 10 MHz and 500
kHz reference, from the counter, and the VFO and CAR in-
stead of a separate HET crystal circuit for each band the TS-
120 uses the counter reference oscillator, and a program-
mable divider circuit contained in the PLL. This simplifies cir-
cuit design and eliminates changes in transmit/receive fre-
quency due to HET crystal frequency deffrences. Fig. 2
shows PLL circuit construction and Table 1 shows the fre-
quency in each circuit.
Referring to Fig. 1, MIX (3) cambines CAR and with VFO
signal and is operated straight through to mixer 1 on 3.5 and
7 MHz. MIX (2) operates at 14 MHz, and above with the
output of MIX (3) to provide mixer 1 input as shown in Table
CENTER
FROMRFAMP || FREQ XTAL
IX(RX) 5 a3miz > | FILTER
PLL UNIT
500KHz
BPF
MIX(TX) IF AMP
COUNTER
UNIT
1. MIX (1) output is filtered amplified shaped and divided by
the programmable divider to obtain 500 kHz output.
The
programmable
divider
converts
the
information
from
the
band
switch
into
a
BCD
signal
in
the
counter.
By
presetting
the
signal
is
divided
at
the
ratio
shown
in
Table
1.
The
phase
comparator
is
a
Motorola
MC4044P.
The
loop
filter
amplifier,
component
transistors,
minimizes
unwanted
spurious
signal.
If
output
of
the
phase
comparator
unlocks,
for
any
reason
VCO
output
is
switched
off
to
prevent
out
of
band
emission
and,
simultaneously
the
digital
display
blanks.
CAR OSCILLATOR
The
CAR
oscillator
contains
one
oscillator
and
two
crystals
for
LSB,
USB,
and
CW
operation.
The
oscillator
frequency
in
each
mode
is
listed
in
Fig.
1.
Oscillator
frequency
can
be
varied
by
the
IF
SHIFT
control
during
reception.
|
|
|
| USB 8.8315 MHz
| LSB = 8.8285 MHz
CW (R) 8.8315 MHz
CW (T) 8.8307 MHz
|
|
x4
Of} (8.8315)
MIX(3) CAR OSC
Of} ‘s.s2e5)
| X2
—a & IF SHIFT
STBY/REC
switch turn VFO
SEND posi-
tion. VFO fre-
quency go up O
to 800 Hz. le: wT)
XTAL
FILTER
|
em
|
MIC
AMP
‘Common part of Rx and Tx.
Fig. 1 TS-120 Frequency configuration

Kenwood TS-120S Specifications

General

Brand	Kenwood
Model	TS-120S
Category	Transceiver
Language	English