Kenwood TS-440S Serivce Manual page 4

TS-440S
CIRCUIT DESCRIPTIO N
1 . Overview
• The TS-440 is a triple conversion type transceiver, incor-
porating a general coverage receiver, which uses 45 .0 5
MHz as the first IF, 8 .83 MHz as the second IF, and 45 5
kHz as the third IF .
• The TS-440 is compact, but allows for installation of a n
optional internal automatic antenna tuner operating in th e
amateur band from 3 .5 MHz to 28 MHz and enables a
wide range of antennas to be used .
• The TS-440 also contains a microprocessor-controlled dig-
ital PLL circuit which controls frequency in 10 Hz step s
using a single crystal oscillator to implement high accura -
cy and stable frequency control .
• The TS-440 has the following major features :
(1) Selectable VFOs ; VFO-A and VFO- B
(2) Direct frequency input using a numeric keypa d
(3) 100-channel memory containing frequency band ,
and mode information (channel 90 to 99 for split fre -
quency memory )
(4) Memory scan in 10 channel groups and two type s
of program sca n
(5) RTTY (AFSK) mode availabl e
(6) Squelch circuit operational in all mode s
(7) Dual filters available to improve selectivity and SI N
ratio (optional filter required )
(8) IF shift, audio notch, IF filter switching, and RF AT T
functions for convenient interference reductio n
(9) Large heat sink and cooling fan (100 W) enabling u p
to one-hour continious transmit operatio n
(101 Full and semi break-in circuits for C W
(1 1) External-computer controllable (optional interface re -
quired )
(12) Many easy-to-read meter functions such as th e
received signal strength (s-meter), transmitter power ,
SWR, and ALC level .
2 . Frequency Element s
The TS-440 utilizes a triple conversion transmitter an d
receiver .
V
30K f IN
RX MIX 1
30MHz , RX
TX
45 .05MHz RX MIX2
8 .83MHz
RX MIX3
455KHz
DE T
DISCR I
RX OUTPU T
TX MIX3
TX MIX I
8 .83MH z
TX MIX 2
SSB,CWT, AM, FM, FSK
(FM MOD )
:45 .O8^-75 .05MH z
-CW R
:45 .0792-- 75 .0492 MHz
SS B
C W
FS K
' AMR,FM R
AMT,FMT : 455KH z
USB, CW
: 456 .5 KH z
-LSB,FSK 453 .5KH z
FSK
AFS INPU T
B .M .
SS B
AM
MIC INPU T
F M
Fig . 1 Frequency configuratio n
The overall frequency configuration of the TS-440 is show n
in Figure 1 . The incoming received signal (f, N
l
is applied t o
the ANT terminal . This signal is mixed with the local oscilla-
tor signal (fvco) in RX MIX 1 to obtain the first IF frequen-
cy . This signal is then mixed with the HET Oscillator signa l
(fHET) in RX MIX 2, to obtain the 2nd IF frequency . Th e
resulting signal is then mixed with the second local oscilla -
tor frequency (f L o) to obtain the 3rd IF frequency . The sig-
nal is then combined with the CAR signal for detection . f i N
is expressed mathematically as follows :
fiN = fvco fHEr – fLo fcAlt
1
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