Kenwood TS-590S, Service Manual

Page: 17 / 162

TS-590S
17
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Transmit power control
Transmit power control is done in the same way as in
the previous models; the ALC circuit controls the ALC volt-
age using the progressive wave voltage (VSF) and keeps a
constant output.
The voltage detected in the Final unit (X45-391 A/2) pro-
gressive wave voltage and reflection wave voltage (VSR)
detection circuits is sent to the TX-RX unit’s (X57-785 A/2)
CN5. The progressive wave voltage is divided into a suitable
voltage by the resistance, and input into the differential am-
plifi ers consisting of Q803 and Q804.
If the progressive wave voltage rises, the emitter volt-
age also rises, and Q804 base current decreases and Q804
collector voltage rises. If this collector voltage exceeds ap-
proximately 2.4V (Q805’s VBE and VE added), Q805’s base
current starts to fl ow, and the collector voltage where the
ALC time constant CR is selected decreases. This collector
voltage is buffered in Q806, the voltage is shifted in D811,
and matched with the keying control voltage by Q807 and
D812 to generate the ALC voltage. If the ALC voltage (2.7V
Fig. 14 Transmit power control
when the ALC voltage is not added) goes down, the IF am-
plifi er’s (Q721) second gate voltage goes down and the gain
is decreased.
When transmitting AM, Q802 is turned on approximately
20ms after transmission, and the ALC voltage is controlled
with the average power. The Q804 base voltage, which
would be ALC’s reference voltage, is controlled by the ad-
justment value (POC) from the main MCU, and output from
pin 5 of the D/A converter (IC13).
SWR protection is controlled by the refl ection wave volt-
age. The refl ection wave voltage is divided by the resistance
and input into IC801. If it exceeds the designated voltage,
IC801’s output controls the ALC voltage and lowers the
power.
The PWR (power) meter is amplifi ed from the progres-
sive wave voltage, the SWR meter is amplifi ed from the re-
fl ection wave voltage, and the ALC meter is amplifi ed from
the ALC voltage each by the relevant operation amplifier
and then input into the A/D converter and displayed on each
meter.
Q805 Q806
Q807
CW
CONTROL
–6V
ALC
OUT
D811
D812
Q803
Q802
VSF
VSR
CURRENT
EXT ALC
IC801
IC802
IC803
ALCREF
CKY
POC
AMC
Q804
8A
DAC (IC75, IC78) and ADC (IC83) Signal Path
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Outline
DAC (IC75) communicates signals with ACC2 and the
Optional unit (VGS-1). DAC (IC78) communicates signals
with USB. ADC (IC83) communicates signals with ACC2/
USB and the Optional unit (VGS-1). The signal path of DAC
(IC75, IC78) and ADC (IC83) vary depending on each status
of transmit/receive.
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Functions relating to transmission
1) Modulation input path
Each output signal from the analog switch (IC80) passes
through the active fi lter (IC81) and then enters ADC (IC83)
and is sent to DSP (IC301).
y
The signal sent from the USB (UAO) is output from pin 6
to pin 5 of the analog switch.
y
The signal sent from the ACC2 (ANI) is output from pin 2
to pin 1 of the analog switch.
y
The message output signal (VAO) from the Optional unit
(VGS-1) passes, without going through the analog switch,
through the active fi lter (IC82), and then input into ADC.
CIRCUIT DESCRIPTION