Kenwood TS-440S Serivce Manual page 7

TS-440S
CIRCUIT DESCRIPTIO N
t
Signals from the ANT pin are fed into the RAT pin of the R F
unit via the transmit/receive switching relay . The signals the n
go to the 10 BPFs through the approx . 20 dB attenuator cir-
cuit, the first stage of the first IF trap circuit, and the lo w
pass filters (which pass only 500 kHz or less) . The signal the n
goes through the second stage of the first IF trap circuit, an d
is mixed with the VCO signal and converted into the first I F
signal of 45 .05 MHz in the first mixer, consisting of Q3 an d
Q4 (2SK125-5) . The VCO circuit consists of Q21 to Q2 4
(2SC2668Y) and oscillates in four bands from 45 .05 MH z
to 75 .05 MHz . Oscillator frequencies are controlled by D C
signals from the PLL unit .
The first IF signal of 45 .05 MHz is passed through the MC F
(F1), which is used in both receive and transmit, and is am -
plified by the first IF amplifier Q5 (3SK74L) . In the secon d
mixer, consisting of Q6 and Q7 (2SK1 25), the first IF signa l
is mixed with the heterodyne oscillator signal (36 .22 MHz )
from the PLL circuit, amplified by Q12 (2SC2668Y) to ob-
tain the second IF signal (8 .83 MHz) . The second IF signa l
of 8 .83 MHz goes through the gate of the noise blanker . I n
modes other than FM , the signal then goes through the MC F
(F2) and is fed into the IF unit through buffer amplifiers Q 8
and Q9 (2SC2668Y) .
1) Selectivity circui t
Figure 4 is a selectivity circuit diagram . In auto mode, th e
appropriate bandwidth filter is automatically selected accord -
ing to mode . When an optional filter is used, two filters ar e
available . Tables 2 and 3 shows the various combinations
When the optional 8 .83 MHz filter is connected, the secon d
IF signal is then fed from the IF unit into the optional filter .
In the third mixer, consisting of Q1 and Q2 (3SK73GR), th e
second IF signal is mixed with 8 .375 MHz signal generate d
by IF unit's heterodyne oscillator circuit, consisting of Q5 3
and Q54 (2SC2458Y), and converted into the third IF signa l
(455 kHz) . The third IF signal is then amplified by Q 5
(3SK73GR) . A diode switch is used to route the signal t o
either the FM or SSB circuits .
In SSB mode, the third IF signal goes through the SSB cer-
amic filter (XF3) . In AM mode, the third IF signal goes throug h
the AM ceramic filter (XF4) . In either mode, the third IF sig-
nal is then amplified by Q7 and Q8 (3SK73GR) and detected .
In FM mode, the third IF signal goes through the FM cerami c
filter (XF5) . The signal is then sent to the FM IF, IC2 (M C
3357) for amplification and detection . IC2 also contains a n
FM noise squelch circuit .
The detected SSB/AM signal is passed through the notch cir -
cuit, consisting of hybrid IC IC1 (BX6124) and squelch gat e
Q12 (2SC2459BL) . The signal then goes through the A F
volume control and is amplified to the appropriate level b y
AF amplifier IC7 (UPC2002V) .
of bandwidth available when optional filters are used . In F M
mode, the selectivity switch does not operate and a singl e
dedicated FM filter is used . Optional filters operate only i n
receive and are separate from the filters used in transmit .
AUTO SELECTIVITY CONTRO L
I
—
X59—1070—00
1
D6
01
I
558 21
,
i
l
a
< ss R
455 3t_
.
14
/a
D I
+
R
+
z
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,$W
I
AI
AL T
D5 02
L aJ
r
p1
<
I
cw R
R4~~
fro m
04
IC 1 0
D4
RYR
D 2
~•
14
i
D3 0 3
Bew
sj
r l
a —i
L_ .
j
J
<A M R
45A 6
L
RX B
45A
I DI I
la
Bow
I
o
D 9
M 2
I4 N -
88 5
455
0
D 5
45S
( -
a
D8
6
SELEC-
TIVIT Y
BBC
AUTO
n
AUT
454
GNDI
F/14 — J
Fig . 4 Selectivity control circuit
MANUAL SELECTIVITY CONTROL
7