the
MAIN
unit.
In
the receive mode, 01 is turned
ON
and
010
is
turned OF F
by
the RSV, and the signal
is
fed
to
the
1st
gate
of
IF amplifier
01,
dual
gate
MOS
FET.
To
the
2nd
gate,
AGC voltage is applied. Its attack time
is
de-
termined
by
R4
and C4.
The amplified 2nd
IF
signal
is
fed
to
the 1st gate
of
the 3rd
mixer
03,
dual
gate
MOS
FET through
02,
which
is
turned
ON
in the receive mode.
To
the 2nd gate, 9.4665MHz local
oscillator signal
for
IF
TUNE
or
PST
is
applied, and the
2nd
I F
signal
is
converted
into
455kHz 3rd I F signal.
In
SSS
or
CW
mode, the 3rd
IF
signal
is
passed
through FI1
mechanical
filter
through
04
and
06,
which
are
turned ON.
M F -455-11
AZ
or
M F -455-11 GZ
is
employed
for
F
Ilo
11
AZ
has
1.5kohm and 240pF
input/output
impedance
and
11GZ
has
1.5kohm and 20pF. Thus, C75 through
C7S
are
not
used
for
the 11GZ.
In
AM mode, the 3rd
IF
signal is
passed
through
FI2
ceramic
filter
through
05
and
07.
The
output
from
the 455kHz filters
is
fed
to
a balanced
mixer consisting
of
04
and
05,
and converted
into
a
9.0115MHz 4th
IF signal again. The local oscillator signal
is
the
same
one
for
the 3rd mixer, and fed
to
the center tap
of
the
input
tuned circuit. The
4th
I F signal
is
fed
to
IF
amplifier
06
through a switching diode
OS,
then amplifier
07.
Soth amplifiers employ dual
gate
MOS FET
res-
pectively.
To
the 1st gate, the
IF
signal
is
fed and
to
the
2nd gate,
AGC voltage
is
applied respectively. The ampl ified
signal
is
fed
to
the OET
UNIT
through J6, Pin 5.
The source voltage
of
OS
is
varied according
to
AGC voltage
i.e., incoming signal level. This voltage
is
amplified
by
07,
then fed
to
the S-meter. R42
is
for
meter zero-point ad-
justment and
R41
is
for
full-scale adjustment.
3 -
1-
4
IF
TUNE
AND
PBT CIRCUITS
The
VXO
circuit
consisting
of
011 and
X1
oscillates at
9.4665MHz, and this frequency
can
be
changed by ± 1.5kHz
by changing the voltage applied
to
013
varactor diode.
This voltage is varied
by
R13, PASS BAND
SHIFT
CONTROL on the
front
panel, and applied
to
013
through
012
in the receive mode. In the transmit mode, a voltage
adjusted
by
R66
is
applied
to
013
through
011,
and
the
oscillation frequency
is
fixed at the center frequency,
9.4665MHz. This signal
is
fed
to
the 2nd
gate
of
03,
3rd
mixer,
and
4th
mixer
04
and
05
through
a.buffer
am-
plifier
012.
When
the
Pass-Band
Shift
Control
is
set
at the center po-
sition, the
VXO
oscillates at 9.4665MHz, and 9.0115MHz,
the center frequency
of
the 2nd I F signal
is
converted
into
455kHz, the center frequency
of
3rd I F signal: This
455kHz signal
is
converted
into
9.0115MHz signal
again
with
the 9.4665MHz
VXO
signal. This
is
the normal con-
dition
of
the
Pass-Band
Shift
system and incoming
signals
pass
through both
pass-bands
of
the filters, 9.0115MHz and
455kHz.
When
the
PB
Shift
Control
is
slid toward the right side, the
VXO
frequency
is
increased,
as
an
example; 9.4675MHz
3-3
(9.4665MHz+1kHz), 9.0115MHz, the center frequency
of
the 2nd IF signal
is
converted
into
456kHz, 3rd
IF
signal.
This 456kHz signal
is
converted
into
9.0115MHz signal
again
with
the 9.4675MHz
VXO
signal. However, the
456kHz, 3rd
IF signal
is
off
from
the center frequency
of
the 455kHz
filter.
In
other words, the
pass-band
of
the
455kHz
filter
is
shifted toward the lower side, and the total
pass-band
is
also shifted toward the lower side.
At
this
time,
if
the optional
SSB
filter
FL-30
is
installed, the total
band
width
is
narrowed
from
the upper side. Thus the
center position
of
the control
is
the widest bandwidth and
is
equivalent
to
the normal
SSB
bandwidth, and the band-
width
is narrowed electrically from either the upper
or
lower
side
continuously
by
up
to
SOOHz.
3
-1
- 5 DETECTOR CIRCUITS
In
the
SSB
and
CW
modes, a 9.0115MHz,
4th
IF
signal
is
fed
to
IC2, product detector in the OET
unit.
To
the other
port
of
IC2, a BFO signal
is
applied and
an
AF signal
is
put
out
from
pin
3.
The BFO
is
composed
of
OS,
X1,
C39, C40, L2 through L4, etc. C39, C40 and L2 through
L4
are
connected in
series
with
X1,
and
L2
through
L4
are
shunted
to
ground respectively according
to
the selected
mode
to
get proper BFO frequency.
The detected
AF
signal
is
fed
to
pin 5
of
IC1
operational
amplifier. The amplified
AF
signal
is
put
out
from
pin 7
and fed
to
07,
low-pass
filter,
then
to
the VOLUME control
on the
front
panel.
IntheAM
mode, the
4th
IF
signal
is
fed
to
01,
IF
amplifier.
A part
of
the amplified signal
is
then fed
to
AM
detector
05.
Toe detected AF signal
is
fed
to
pin 3
of
IC1, operational
amplifier. The amplified
AF
signal
is
put
out
from
pin
1
and then fed
to
low-pass
filter
07.
As
an
AGC voltage, a part
of
the
4th
IF
signal
at
01
col-
lector
is
fed
to
AGC detector
01.
The detected
DC
signal
is
then fed
to
the
base
of
02.
When
the applied voltage
is
over the threshold voltage,
02
is
turned
ON
and a negative
voltage connected
to
the emitter,
charges
C6
through R9.
When
the applied voltage
becomes
less
than threshold
voltage,
or
zero,
02
is
turned OFF and the voltage
of
C6
is
discharged through
RS
(high value resistor). This provides
fast attack/slow
release
AGC. AGC voltage
is
taken
from
the collector
of
02
and supplied
to
each
2nd gate
of
the
I F amplifiers.
On
the AGC line, the
RF
gain control voltage
from
the
RF
GAIN
control
is
superimposed.
When
the AGC switch on the
front
panel
is
pushed in,
010
is
turned ON, and R13 and C10 (in
series)
are
connected
in parallel
with
RS
and the AGC time constant
becomes
shorter.
3 - 1 -6
AF
POWER
AMPLIFIER
CIRCUIT
AF signal
from
the VOLUME control,
RS-2,
on the
front
panel
is
fed
to
pin
1
of
IC1
AF
povver
amplifier on the
MAIN
unit.
The signal
is
amplified
with
IC1
to
get 2 watts
output
power in
an
S ohm load. The
output
signal
is
fed
to
the internal speaker through the PHONES jack and EX-
TERNAL
SPEAKER jack. This IC
is
activated in the
transmit mode
to
produce the
CW
side-tone.
for
free
by
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