TKR-850
11
1. Outline
The TKR-850 is a UHF/FM repeater designed to operate in
the frequency range of 400 to 512MHz.
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 430
MHz (K3).
The receiver circuit located in TX-RX unit (X57-696 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 470MHz (E), 450 to 480MHz (K), 480 to 512MHz (K2) or
400 to 430MHz (K3), with a passband of 5.0MHz.
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 local
oscillator signal from the PLL frequency synthesizer circuit at
the first mixer DBM (A1) to become a 44.85MHz first inter-
mediate frequency (IF) signal. The first IF signal is fed
through two monolithic crystal filters (XF2; Wide, XF1; Nar-
row) to further remove spurious signals.
W/N
SQL
DET
TX-RX unit (X57 A/2): TX-RX
SW
SW
W/N
W/N
MCF (Narrow)
XF1
MCF (Wide)
XF2
RSSI
QUD
W/N
SW
DET
VCO A
VCO B
RX VCO
A3 (X58-480)
RX ANT
BPF
L2
RF AMP
Q1
BPF
L4,L5
1st MIX
DBM A1
IF AMP
Q8
IF AMP
Q9
IF AMP
Q10
LPF
IF AMP
Q2
44.85MHz
D1
D2
IF AMP
Q3
FM SYSTEM IC
IC9
SW
SW
NOISE DET
D5
NOISE AMP
Q7
D3
D4
X1
44.395MHz
CF1 (Wide)
CF2 (Narrow)
Q4
f
RX
–44.85MHz
DEI DEO
RD
CODEC
RA
RXI RXO
DAC
AMP
IC608
AMP
IC619 (B/2)
LPF
IC619 (A/2)
AINR
AOUTR
CPU
IC614
IC604
IC615
SW
IC622
MUTE
Q606
AM
SPM
AF
AMP
INT SP
IC629
RSSI
ASQ
TX-RX unit (X57 B/2): Control
455kHz
44.850MHz
IC621
Q605
INV
Fig. 1
Receiver circuit
CIRCUIT DESCRIPTION
