Circuit Description; Overview; Circuit Configuration By Frequency; Receiving System - Kenwood TK-940 Service Manual

CIRCUIT DESCRIPTION
I
1. Overview
2. Circuit Configuration by Frequency
This transceiver is an 800MHz-band (TK-9401,
The receiver
I S
a double-conversion superhet w i t h a
9OOMHz-band (TK-941) EFJ LTRrM trunked-system- first intermediate frequency (IF) of 45.0375MHz (TK-
compatible FM
transceiver
that can be programmed t o 940), 39.0375MHz (TK-941) and a second IF of 455kHz.
operate on both LTR and conventional systems.
Incoming signals from the antenna are mixed with the
local signal from the PLL t o produce the first IF of
45.0375MHz (TK-940), 39.0375MHz (TK-941).
This is then mixed with the 44.5825MHz (TK-940),
38.5825MHz (TK-941) second local osclllator output t o
produce the 455Hz second IF. This is detected t o give
the demodulated signal.
The transmit signal frequency is generated by the
PLL VCO, and modulated by the signal from the micro-
phone. It is then amplified by TX amplifier and PA
amplifier, and sent t o the antenna.
I
CF
ANT TK-940 TK-941 455kHz
TX 806-825MHz T X 896-902MHz
851 -870MHz 935-941MHz
RX 851-870MHz RX 935-941MHz
1st M I X MCF
Fig. 1 Frequency configuration
ANT RF
'
IF SYSTEM
-
SW AMP
805.9625-824.9625MHz.: TK-940
3. Receiving System
3-1.
RF
unit
An incoming RF signal from the antenna terminal
passes through the antenna switch (D19, D20, and
D21 are off) and then the bandpass filter (L9). The
signal is ampliked by RF amplifier 0 2 4 , and passes
through the bandpass filter (L6) again. The resulting
signal goes to the flrst mixer (021), where it is mixed
with the first local oscillator signal output from the
frequency synthesizer t o produce t h e f i r s t IF
45.0375MHz (TK-9401, 39.0375MHz (TK-941).
3-2. IF unit
The flrst IF s~gnal then passes through a four-pole
m o n o ~ t h l c crystal flter (XFI
The s~gnal 1 s ampllfled by
flrst IF amplrf~er 0 1 6 and goes t o the second IF unlt
The second IF unit cons~sts of an IF system IC
( I C ~ )
and the second mlxer, second local osclllator, second
IF fllter, and FlV detector, tC7 mlxes the slgnal Input t o
~t w ~ t h the 44 5825MHriiTK-940), 38 5825MHz (TK-
941) second local osclllator output #f the clystal
osclilator (X2) to produce the second IF
c' '55kk
The 455kHz slgnal then goes throug
55khL ce-
ramic filter CFI, is amplifl 5y the Ilm ampllfler,
demodulated by the quac re F M de or (In the
same
IC),
and output t o tht elve audlo
,
l p l ~ f ~ e r
AF
AMP
MIC
AMP
- -
S P
A
45.0375MHz : TK-940
-
TK-940 TK-941
806-825MHz 896-902MHz
851-870MHz 935-941MHz
I
PLL
VCO
44.5825MHz : TK-940
39.0375MHz : TK-941
38.5825MHz : TK-941
-
MIC
AMP