Functional Description - 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.
CAR OSCILLATOR
|
|
|
| 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