Circuit Descriptio; General Description; Transmitter Section; Receiver Section - Kenwood TS-680S Instruction Manual

5. CIRCUIT DESCRIPTION
5-1. GENERAL DESCRIPTION
The TS-140S/680S utilizes double-conversion for
FM transmissions, and triple-conversion for all other
transmission modes, and for all modes in receive.
The intermediate frequencies are 40.055 MHz and
455 kHz.
A wide dynamic range is made possible thru the use
of 2SK125 junction FET's in the receiver section's
1st and 2nd mixers.
An integrated circuit balanced modulator
(SN16913) is used in the 1st transmitter mixer and
3SK122 is used in the 2nd mixer. The PLL circuit,
consisting of 4 loops, and the digital VFO are con-
trolled by a single reference oscillator circuit. IF
SHIFT and 10 Hz tuning steps are provided thru the
use of this system.
5-2. TRANSMITTER SECTION
The incoming microphone audio is routed to the SW
unit where it is amplified by the microphone amplifier
and then distributed to the SSB, FM and VOX cir-
cuits. (VOX circuit is TS-140S only.)
The amplified SSB audio signals are canverted inta a
455 kHz DSB (Double Sideband) signal by the
balanced modulator {AN612). The signal is then
filtered by a ceramic filter in order to abtain the
desired SSB signal. This signal is then mixed with a
local ascillator signal of 39.6 MHz by the first mixer
which results in a 40.055 MHz signal. This signal is
filtered by a monolithic crystal filter (MCF) and com-
bined with the VCO frequency, in the 2nd Mixer, to
obtain the final transmit frequency. In FM the
microphone audio signal is amplified and used to
directly modulate the 39.6 MHz local gscillator. This
FM signal is then mixed with the VCO signal to ob-
tain the final transmit frequency. The SSB and FM
signals enter the final unit for amplification to the
final output power level. This signal is applied to the
Low Pass Filter where unwanted spurigus com-
ponents are removed before actual transmission.
5-3. RECEIVER SECTION
The incoming signal for the antenna is fed to the
receive band-pass filters in the signal unit, via a front
panel controlled attenuator circuit.
The appropriate bandpass filter is automatically
selected based upon control information supplied by
the Control Unit. Independent RF amplifiers are also
included for the 28, and 50 MHz bands and can be
turned OFF or ON via a front panel control. (TS-680S
only)
Signals from the BPF are mixed with the VCO signal
in the 1st RX mixer to obtain the 1st IF frequency of
40.055 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 HET OSC frequency of 39.6 MHz to obtain
the 2nd IF frequency of 455 kHz.
28
This signal is separated and applied to two different
areas. One is used to control the operation of the
Noise Blanker. The other signal passes the Noise
Blanker gate is amplified, and passed thru the ap-
propriate IF filter. The SSB, CW, and AM signals are
amplified further and then demodulated by their
respective detector circuits. The FM_ signal is
amplified and detected in a custom IC.
5-4. CIRCUIT BOARD DESCRIPTION
The 1S-140S/680S contains the following major
units: Signal unit, Control unit, Filter unit, Final unit,
Display unit, Switch unit, etc. A brief description of
these units follows.
5-4-1. Signal Unit (X57-3190-00, 3200-10)
The signal unit is composed of the transmit and
receive sections. These consists of the Signal
system amplifiers, mixers, detectors, modulators,
filters, VCO's, and the various timing circuits used
for transmit/receive switching. This unit handles
practically all TS-140S/680S signal processing.
§-4-2. Control Unit (X53-3100-11, 12)
The control unit is composed of the frequency con-
trol section which is controlled by a microprocessor
and four PLL loops. The unit also contains a
reference oscillator, operating at 36 MHz, which is
the reference for all frequencies generated by the
transceiver,
5-4-3. Display Unit (X54-3050-00}
The display unit consists of a fluorescent display
tub, LED indicator section, DC to DC converter, and
various switching circuits.
5-4-4. Final Unit (X45-3100-00, 11)
This unit amplifies the TX RF signal for transmission.
This is accomplished by utilizing a three-stage final
amplifier section having a relatively low collector
loss figure, and a high efficiency cooling system.
5-4-5. Fitter Unit (X51-3040-00, 11}
The filter unit removes the undesirable spurious high
frequency components from the transmitter output.
4 50 MHz power module is also included in this sec-
tion for the TS-680S.
5-4-6. Switch Unit (X41-3030-00, 11)
The switch unit includes the speech processor and
the MIC amp circuit.