Circuit Description - Kenwood TKR-850 Service Manual

TKR-850
1. Outline
The TKR-850 is a UHF/FM repeater designed to operate
in the frequency range of 440 to 470MHz (E), 450 to
480MHz (K), 480 to 512MHz (K2) or 400 to 430MHz (K3).
The unit consists of receiver, transmitter, phase-locked
loop (PLL) frequency synthesizer, and control circuits.
2. Receiver Circuit
The receiver is double conversion super-heterodyne, de-
signed to operate in the frequency range of 440 to 470MHz
(E), 450 to 480MHz (K), 480 to 512MHz (K2) or 400 to
430MHz (K3).
The receiver circuit located in TX-RX unit (X57-627 A/2)
consists of the following : 2-1 front-end circuit, 2-2 first
mixer, 2-3 IF amplifier circuit, 2-4 audio amplifier circuit, and
2-5 squelch circuit.
2-1. Front-end Circuit
The front-end circuit consists of BPF L2, RF amplifier Q1,
and BPF L4/L5. The helical BPF covers frequency ranges
440 to 480MHz (K,E) and 480 to 512MHz (K2) with a pass-
TX-RX unit (X57 A/2): TX-RX
RSSI
Q4
DET
NOISE DET
SQL
TX-RX unit (X57 B/2): Control
DEI DEO
RD
ASQ
RSSI
18

CIRCUIT DESCRIPTION

MCF (Wide)
XF2
IF AMP
Q3
D2
D1
MCF (Narrow)
SW
SW
XF1
W/N W/N
44.850MHz
FM SYSTEM IC
IC9
SW QUD
CF1 (Wide)
W/N
SW
D4
D5
DET
CF2 (Narrow)
NOISE AMP
455kHz
Q7
AMP AMP
IC614
IC608 IC619 (B/2)
CODEC
AINR
AOUTR
IC604
CPU
Fig. 1 Receiver circuit
band of 5.0MHz, 400 to 430MHz with a pass band of
3.0MHz (K3).
The BPF L4/L5 attenuates the unwanted signals, and
sends only the necessary signal to the first mixer DBM A1.
2-2. First Mixer
The signal from the BPF is heterodyned with the first lo-
cal oscillator signal from the PLL frequency synthesizer cir-
cuit at the first mixer DBM (A1) to become a 44.85MHz first
intermediate frequency (IF) signal. The first IF signal is fed
through two monolithic crystal filters (XF2; Wide, XF1; Nar-
row) to further remove spurious signals.
2-3. IF Amplifier
The first IF signal is amplified by Q2 and Q3, and then
enters IC9 (FM system IC). The signal is heterodyned again
with a second local oscillator signal (44.395MHz) with in IC9
to become a 455kHz second IF signal. The second IF signal
is fed through a 455kHz ceramic filter, CF1 (Wide), CF2 (Nar-
row) to further eliminate unwanted signal, and the quadra-
ture detection circuit FM-detects the signal to produce a
base-band signal and output it from pin 11.
44.85MHz
BPF
IF AMP 1st MIX
L4,L5
Q2 DBM A1
IF AMP
LPF
Q10
X1
44.395MHz
SW
D3
W/N
LPF
RXI RXO IC615
IC619 (A/2)
DAC
RA
IC621
AM
SPM
BPF
RF AMP
L2
Q1
RX VCO
A3 (X58-480)
IF AMP IF AMP
Q9 Q8
VCO A
VCO B
f –44.85MHz
RX
IC629
IC622 Q606
AF
SW
MUTE
AMP
INV
Q605
INT SP
RX ANT