Transmitter; Antenna Tuner - Kenwood TS-940S Instruction Manual

10-4. TRANSMITTER
The audio signal from the microphone is applied to the IF
unit MIC terminal and is preamplified by 036. The output
is applied to the MIC GAIN control (on the front panel), the
FM MIC GAIN control (on the top panel) or VOX circuit in
the SSB and AM modes. The SSB signal channel is re-
turned to the IF unit, amplified by IC3 and applied to ba-
lanced modulator D73. A diode switch is provided at the
input of IC3, which selects the audio signal in the SSB and
AM mode, and the AFSK signal (2.2936 kHz/2.1277 kHz)
from the PLL unit in the FSK mode. Balanced modulator
D73 is constructed as a package containing four matched
Schottky diodes, which provides stable modulation char-
acteristic against varying operating conditions such as
temperature fluctuation. The 455 kHz DSB (Double Side
Band) signal from D73 is converted to SSB by filter CF1
(or CF2 in the AM mode), which is shared by the third re-
ceiver IF filter after passing through the buffer amplifier
037.
The filter output runs through buffer amplifier 039 and is
then applied to the RF speech processor circuit 040, IC4
and 043. When the processor is off, the signal is applied
directly to the first transmitter mixer 044 and 045 via
diode switch D78 and D79. In FSK mode, even if the pro-
cessor switch is off, approx. 1 OdB compression is auto-
matically applied. This effectively suppresses any level dif-
ference between MARK and SPACE frequencies in AFSK.
Note, however, that the compression meter does not de-
flect.
In the AM mode, even if the processor switch is off, the
signal runs through D78 and D79 but does not pass
through the processor. The processor output signal is ap-
plied to the first transmitter mixer via diode switch D83.
Here, the audio signal is mixed with the CAR2 signal
(9.285 MHz) and converted to 8.83 MHz. The 8.83 MHz
signal runs through SSB filter XF2 (a wide band filter L37,
L38 or optional YK-88A-1 in AM mode) shared by the se-
cond receiver IF filter, where any splatter which may be
generated in the speech processor is eliminated.
The signal is then applied to the transmitter IF amplifier
048. In CW and FM modes or during auto antenna tuning,
the CARO signal is applied to 048 via buffer amplifier
046. In these modes, since the transmitter signal does
not pass through the narrow band filter, full CW break-in
operation is enabled.
The transmitter signal is then applied to the second trans-
mitter mixer 050 and 051, where it is mixed with the HET
signal (36.22 MHz), yielding a TIF signal at 45.05 MHz,
whose output is connected to the RF unit. In the RF unit
the signal is mixed with the VCO signal in the third trans-
mitter mixer 01 and 02, providing the final transmitter fre-
quency.
Any undesirable components in this signal are then elimin-
ated in the transmitter BPF (1.8 - 30 MHz). The signal
is amplified by wideband amplifier 03, 04 and 05 and
supplied from the DRV terminal to the Final unit as the
drive-level output. This drive output is automatically dis-
connected from the Final unit input if a plug is inserted into
the transverter connector. The signal applied to the Final
unit is amplified by wideband drivers 02, 03 and finals 04,
05.
The output of the Final unit passes through the Filter unit
where the unwanted higher harmonic component ele-
ments are eliminated. The Filter unit divides the transmit-
ter frequency range into bands. Each LPF is automatically
selected by TX LPF information (LPO-LP2) supplied from
Digital unit A.
After passing through the Filter unit, the transmitter output
runs through the AT (optional) unit, the transmitter/
receiver selector circuit and then is connected to the ANT
terminal on the rear panel.
10-5. AUTO ANTENNA TUNER
The auto antenna tuner consists of the tuner section and
the control section.
The tuner section consists of coils and variable capacitors
which form the matching circuit. The variable capacitors
are driven by high speed motors.
The control section decodes the matching condition of the
transmitter output stage and drives and controls the mo-
tors to make a good match between the transmitter and
the antenna.
This auto antenna tuner works within the amateur bands
(1.8 MHz
~
29.7 MHz).
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