The
signal
amplified
by
04
and
05
is
fed
to
the FI L (low-
pass
filter)
unit
throu{ll
L8
impedance matching trans-
former.
A thermal switch
is
mounted on the
case
of
04
and turns
ON
when the
case
temperature exceeds 70
degrees
C.
This
changes
the
speed
of
the cooling fan from
low
to
high. This
cooling fan rotates at
low
speed
during transmit in the
normal condition.
At
this time, 8 volts
is
supplied
to
the
fan
motor
through R22, R23
and
07.
When
the thermal
switch
is
turned ON, 13.8 volts
is
supplied
to
the fan
motor
through R22
only,
and the cooling fan rotates at high
speed
not
only in the transmit mode
but
also in the receive mode.
The transmit
signal
which
has
passed
the low-pass
filter
is
fed
to
the
ANT
(antenna) connector on the rear
panel
through the
SWR
detector coil L 15 in the FI L
unit.
3 - 2 - 4
ALC
CIRCUITS
The foward power voltage,
SWF
and reflected power
voltage,
SW8, detected at the F I L
unit,
are
fed
to
the
MAIN
unit
through J20. The foward power voltage, SWF,
is
fed
to
the negative input terminal
of
IC28 and amplified
as
an
ALC voltage. This ALC voltage
is
fed
to
the 2nd
gates
of
09
in the
MAIN
unit
and
07
in the
RF
unit.
In the
SS8
or
CW
mode, the attack time
of
the ALC
voltage
is
determined
by
R70, C43
and
R 169
and
the
release
time
is
determined by C43
and
R88, and a
peak
voltage
is
put
out. -
In
the AM mode,
013
and
014
are
turned ON,
and
the
attack time
is
determined
by
R70
and
C42, and the
release
time by R68 and C42, and
an
average
voltage
is
put
out.
To the positive terminal
of
IC28, a voltage from the
RF
POWER
control on the
front
panel
is
applied
to
control
the
ALC
voltage
and
the
output
power
can
be
adjusted
between 10 watts
and
100 watts
by
adjusting the
RF
POWER
control.
The
ALC
voltage
is
also
fed
to
the negative terminal
of
IC38 through R88
and
amplified
to
indicate
ALC
level
on
the meter. The swing
of
the meter
is
adjusted
by
R91.
The voltage applied
to
the negative terminal
of
IC28
is
controlled by the
RF
POWER
control on the
front
panel.
When
the control
is
turned
fully
counterclockwise, the
voltage
is
minimum and the
output
power
is
also
miminum
(10 watts). This voltage (output power)
can
be
adjusted
by R149.
When
the control
is
turned
fully
clockwise, the voltage
is
the maximum
and
the
output
power
is
also the maximum
(SSB
and
CW:
100 watts, AM:4O watts). This voltage
is
divided from 8 volts by R147
and
R150,
and
can
be
ad-
justed
by
R 150.
In
the AM mode,
019
is
turned
ON
and
R151
is
connected
with
R150 in parallel,
and
the maximum power
is
reduced
to
40 watts.
3-5
S3
is
a switch
to
reduce the maximum power toOO watts.
When
S3
is
switched ON, a voltage
is
applied
to
the
base
of
019
through
028
and R153
and
019
is
turned ON the
same
as
in the AM mode. In addition, a voltage
is
applied
to
the R F
POWE
R control through R 168 and
029,
and the
maximum power
is
adjusted
to
50 watts by R168. In the
AM mode,
020
is
turned
ON
and
R168
is
shunted
to
ground and the maximum power
is
40 watts
as
usual.
3 - 2 - 5
VOX
CIRCUITS
Audio
signal
from the microphone
is
fed
to
pin 5 (positive
input
terminal)
of
IC6, comparator, through J3 and R137,
VOX
GAIN
control. To pin 5, a
bias
voltage which
is
divided by R132
and
R135,
and
R136
is
applied through
R137.
To_
pin 6 (negative
input
terminal), a reference
voltage which
is
divided by R132,
and
R135
and
R136
is
applied. The difference voltage between the
two
terminals
is
only
the voltage
across
R135. Thus the sensitivity
of
the
comparator
is
very high
and
the
VOX
circuit actuates with
a small input level.
When
a voice signal presents, the
output
terminal (pin 7)
of
IC6B
becomes
at High level and this
voltage
charges
C63. The charged voltage
is
discharged
through R128 and R129 and
it
decides the VOX holding
time. The
VOX
holding time
can
be
adjusted by R129.
This High level voltage
is
applied
to
pin 5 (positive input
terminal)
of
IC5B,
VOX
control.
In the
CW
mode, IC5A
is
used
as
a break-in control.
In the key-up condition, the
same
bias
voltage
is
applied
to
both pin 2 (negative input terminal) and pin 3 (positive
input
terminal), and pin 1
(output
terminal)
is
low level.
In the key-down condition, pin 2
is
grounded through
R117 and pin 1
becomes
at high level. This voltage
charges
C62
and
is
applied
to
pin 5
of
IC5B. The holding time
is
decided by C62,
and
R128 and R129.
To
pin 6
of
IC5B, a bias voltage divided by R125 and R139
is
applied
as
a reference voltage.
When
the voltage at pin 5
becomes
higher than that
one
at pin 6, pin 7
(output
terminal) puts
out
high level voltage. This turns on
017
and
018,
and
grounds the SEND line, when the
VOX
switch
is
turned on,
to
set the radio in the transmit mode.
3 - 2 - 6
ANTI
VOX
CIRCUITS
A part
of
the receiver audio signal
put
out
from
IC1
is
fed
to
pin
3 (positive input terminal)
of
IC6A, comparator,
through the
ANTI
VOX
level control, R142.
When
a
re-
ceiver audio
is
present, pin 1
of
IC6A puts
out
high level
voltage. This voltage
is
applied
to
pin 6
of
IC5B, and in-
creases
the reference voltage and cuts
off
IC5B. Thus the
VOX
circuit
does
not
function
with
an
audio from the
speaker.
for
free
by
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