Kenwood TS-440S - Manual (Page 22)

4. CIRCUIT DESCRIPTION
4-1. GENERAL DESCRIPTION
The TS-440S utilizes double-conversion for FM trans­
missions, and triple-conversion for all other transmis­
sion modes, and for all modes in receive. The
intermediate frequencies are 45.05 MHz, 8.83 MHz
and 455 kHz.
A wide dynamic range is made possible thru the use
of 2SK125 junction FET's in the receiver section's 1 st
and 2nd mixers, and by a 3SK73 dual-gate MOS FET
in the 3rd mixer.
An integrated circuit balanced modulator (AN612) is
used in the 1st transmitter mixer and 2SK122's are
used in the 2nd and 3rd mixers. The PLL circuit, con­
sisting of 5 loops, and the digital VFO are controlled
by a single reference oscillator circuit. IF SHIFT and 10
Hz tuning steps are provided thru the use of this
system.
4-2. TRANSMITTER SECTION
The incoming microphone audio is routed to the IF unit
where it is amplified by the microphone amplifier and
then distributed to the SSB, FM and VOX circuits. The
SSB signal is applied to the balanced modulator, then
amplified and converted to the 1st IF frequency of 455
kHz. This DSB (Double Side Band) signal is filtered to
obtain the SSB signal. The SSB signal is mixed with
the local oscillator frequency of 8.375 MHz in the 1st
mixer to obtain the 2nd IF signal of 8.83 MHz. This
signal is filterd by a CF (Ceramic Filter) to remove the
unwanted by-products of the mixing action. The
filtered output is applied to the RF unit.
In the RF unit the signal is mixed with the НЕТ OSC
frequency of 36.22 MHz by the 2nd mixer to obtain
a frequency of 45.05 MHz. This signal is combined
with the VCO signal in the 3rd mixer to obtain the
transmit frequency which is applied to the Final unit
via a LPF (Low Pass Filter). The Final unit amplifies the
signal to the desired power level and then routes the
signal thru an additional LPF to the antenna terminal,
or the Antenna Tuner, if installed.
4-3. RECEIVER SECTION
The incoming signal for the antenna is fed to the
receive band-pass filters in the RF unit, via a front panel
controlled attenuator circuit. Selection of the desired
BPF is accomplished thru data supplied from the Con­
trol unit. Signals from the BPF are mixed with the VCO
signal in the 1 st RX mixer to obtain the 1 st IF frequen­
cy of 45.05 MHz This signal is filtered by a MCF
(Monolithic Crystal Filter) and applied to the 2nd RX
mixer. This mixer combines the 1st IF frequency with
the НЕТ OSC frequency of 36.22 MHz to obtain the
2nd IF frequency of 8.83 MHz.
The 2nd IF frequency is split into two paths, one to
the noise blanker circuits, and the other past the noise
blanking gate to the 2nd IF filter. The signal that is
taken from the output of the 2nd IF filter is applied to
the 3rd RX mixer, via a buffer amplifier, where it is
mixed with the local oscillator frequency of 8.375
MHz, to obtain the 3rd IF frequency of 455 kHz.
This 3rd IF frequency is either amplified and then
demodulated by the FM detector 1C, for FM operation,
or applied to the 455 kHz filter. After filtering the sig­
nal is amplified and applied either to the SSB or AM
detector circuits.
4-4. CIRCUIT BOARD DESCRIPTION
The TS-440S contains the following major units;
RF unit, IF unit. Control unit, PLL unit. Filter unit, AT
unit, etc. A brief description of these units follows.
4-4-1. RF unit (X44-1680-00)
The receive section of this unit includes the BPF's for
each band, the 1st RX mixer, a 45.05 MHz MCF, the
2nd RX mixer, noise blanker circuits, and an 8.83 MHz
MCF. The transmit section includes the 2nd TX mix­
er, 3rd TX mixer, amplifier circuits, FM microphone am­
plifier circuit, microphone limiter circuits, and four
VCO's required to cover the frequencies from 100 kHz
to 30 MHz.
4-4-2. IF unit (X60-1300-00)
The receive section of this unit contains the 8.83 MHz
filter, 3rd RX mixer, 455 kHz filter, detector, and low
frequency amplifiers. The transmit section contains the
microphone amplifier, balanced modulator, 1st TX mix­
er, 8.83 MHz filter, etc. This unit also includes the tim­
ing circuit which controls the CW break-in circuit, and
the 8.375 MHz local oscillator circuit.
4-4-3. Control unit (X53-1450-00)
The unit is centered around the main microprocessor,
and provides a wide variety of control signals for all
the various units.
4-4-4. PLL unit (X50-2050-00)
Five PLL loops are provided, as well as the reference
crystal oscillator (36 MHz).
4-4-5. Final unit (X45-1470-00)
This unit amplifies the TX RF signal for transmission.
TS-440S has an output of 100 W. This is accomplished
by utilizing a three-stage final amplifier section having
a relatively low collector loss figure, and a high effi­
ciency cooling system.
4-4-6. Filter unit (X51-1340-00)
Provides for a high quality transmitter output by reduc­
ing unwanted harmonic emissions. This unit also de­
tects the forward and reflected power sensing circuits
for ALC, SWR and Antenna Tuner circuits.
4-4-7. Automatic Antenna Tuner unit (X57-1150-00)
This unit consists of the tuner and control sections. The
tuner section consists of three coils and motor driven
variable capacitors which form the actual tuning cir­
cuit. The control section takes the information provid­
ed by the filter unit, as well as band and frequency data
provided by the RFunit to control the variable capaci­
tors, and switching off the coil. The automatic anten­
na tuner operates from 3.5 thru 29.7 MHz.
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