Circuit Description - Kenwood TM-V708A Service Manual

1. Frequency configuration
The TM-V708A has an individual VCO and PLL unit for
both VHF and UHF bands. Using these separate VCO and
PLL circuit, it can receive 2 separate bands at the same time.
Also, you can perform the full-duplex operation.
The VHF VCO is used for the following functions:
(i) VHF transmission
(ii) The first local oscillator for the main band (VHF) reception.
(iii)The first local oscillator for the sub band (UHF)
reception (doubled).
MIC
MIC AMP
Crystal
12.8MHz
12.8MHz
OSC
SP
AF AMP
A 438.000~449.995MHz
B 438.000~439.995MHz
C 144.000~147.995MHz

CIRCUIT DESCRIPTION

PLL 1 VCO 1
2nd IF
455kHz
AF
DET
OSC
Crystal
Crystal
45.505MHz
12.8MHz
PLL 2 VCO 2
2nd IF
450kHz
AF
DET
38.4MHz
3
D 144.000~147.995MHz
E 144.000~145.995MHz
F 438.000~449.995MHz
Fig. 1 Frequency configuration
The UHF VCO is used for the following functions:
(i) UHF transmission
(ii) The first local oscillator for the main band (UHF) reception.
(iii)The first local oscillator for the sub band (VHF)
reception (halved).
The PLL reference frequency is generated by a 12.8MHz
crystal oscillator connected to the VHF and UHF PLL ICs. This
reference frequency is used for both PLL circuits.
The second local oscillator for the VHF band uses the
tripled 12.8MHz reference oscillator frequency. The
45.05MHz second local oscillator for the UHF band is
generated by the IF IC crystal oscillator circuit.
H
1/2
1st IF
45.05MHz
IF 1
I
K
2
1st IF
38.85MHz
IF 2
L
G 392.950~404.945MHz
H 378.100~382.090MHz
I 189.050~193.045MHz
TM-V708A
A
UHF TX
G
MAIN
UHF RX
B
SUB
C
VHF RX
D
VHF TX
J
MAIN
VHF RX
E
F
SUB
UHF RX
J 182.850~186.845MHz
K 195.575~200.5725MHz
L 399.150~411.145MHz
ANT
3