it
is
shaped
into
apulsed wavefonn occuring
at
a
period
of
one
fourth
the
100 kHz and drives a
free-running multivibrator consisti.ng
of
transistors
Q2 and Q3 at aperiod
of
just
25
kHz since the
multivibrator has afree-running period
of
about
25
kHz.
The
output
of
the
multivibrator
is
applied to
amplifier transistor Q4,
through
which
it
is
shaped
in the rectangular wavefonn and delivered to
RF
amplifier Q1 in the
RF
Unit.
When
the
FUNCTION switch
is
placed in the
100 kHz CAL position
the
emitter
of
transistor Q2
is
grounded via
the
MS
terminal
of
this unit,
turning transistor Q2 off. This disables the multi-
vibrator
and
allows transistor Q3
to
operate as a
mere amplifier. As aresult,
the
100 kHz pulsed
signal from
the
oscillator transistor are
conducted
as
they
are to amplifier transistor Q4 and, there-
fore,
to
RF
amplifier Q
1.
7.
Regulated
Power
Supply Unit (UC1010J)
The
regulated
power
supply
unit
provides
necessary operating voltages for the VFO, BFO and
1st local oscillator. Especially,
it
supplies avoltage
with least variation to
the
VFO (including the
RIT
circuit)
to
prevent
the
VFO from changing its
oscillator frequency with variation
of
the supply
voltage.
The
unit
consists mainly
of
four transistors Q1
(2SA497),
Q2
(2SC373), Q3 (2SC372) and Q4
(2SC372) and reference diode D1 (RD6A).
Transis
tor
Q1
is
the current
con
trol transistor,
which controls the
input
current
in accordance
with
an
error
voltage. Transistors Q2 and Q3 are
the
error
voltage amplifier transistors. Transistor
Q4
is the
error
voltage
detector
transistor and also
serves as
the
temperature-characteristic cancelling
transistor for transistor Q3. Diode D1 (RD6A) is
the
zener diode for producing areference voltage.
The
error
voltage
detected
by
error
voltage
detector
Q4
is
amplified
through
two amplifier
stages
of
transistors
Q2
and Q3. This allows
the
regulated
power
supply
unit
to
provide
an
ex-
tremely excellent voltage stability.
The
voltage stability due
to
a
temperature
change depends
on
the
temperature
characteristics
of
the reference voltage diode and the error voltage
amplifIer circuit.
The
reference voltage diode used is zener diode
RD6A, which has a
temperature
coefficient
of
O.
7
While,
the
error
voltage amplifier circuit consists ot
amplifier transistors Q2 and Q3 with transistor Q3
coupled
through
differential
connection
to
error
voltage
detector
diode Q4, and offers least varia-
tion
of
its characteristic due
to
temperature
change
because transistors Q3 and
Q4
cancel their tem-
perature characteristics.
Further,
current
control
t,dnsistor Q1 suffers from
almost
no
change
of
its
characteristic due
to
temperature change because it
is
asilicon PNP transistor.
In
addition,
this regulated power supply
unit
is
so arranged
that
it
protects
current
control
transis-
tor
Q1 against
an
excessive currentwhich might be
flowed through
the
transistor when the
output
terminal
is
shorted
to earth, as
encountered
in
ordinary regulated
power
supply circuits.
Resistors RIO
and
R
11
and variable resistor
VR2 are provided to
produce
necessary
RIT
voltages
to
be fed
to
the
RIT
circuit in
the
VFO
unit.
8. AF Unit (UC1307J)
The
AF
unit
incorporates
an
AF
amplifier
circuit to
operate
the
speaker. This amplifier
circuit amplifies
the
AF
output
delivered via
variable resistor
VR4
(l0
kn),
or
the
AF
volume
control, from squelch
buffer
transistor Q7, which
is
connected
through the MODE switch and detec-
tor
circuits to 2nd
IF
amplifier transistor Q3.
The
AF
amplifier circuit, consisting mainly
of
four amplifier transistor Q1 (2SC733), Q2
(2SC734), Q3 (2SD90) and
Q4
(2SB473), operates
as follows:
The
AF
signal from squelch
buffer
transistor
Q7
is
conducted
from
the
IN terminal
of
the unit
via capacitor
Cl
to
amplifier transistor Q
1,
where
the
signal
is
amplified on
the
voltage amplification
basis.
The
output
of
amplifier transistor
Ql
is
amplified by amplifier transistor Q2 on
both
the
voltage and
power
amplification bases.
The
output
signal from amplifier transistor Q2
is
applied to a
power
amplifier consisting
of
transistors Q3 and
Q4, where it
is
amplified
on
the
power
amplifica-
tion basis. Since transistors Q3 and
Q4
are coupled
through a
comprementary
connection
circuit to
the
preceding circuit,
they
form an
output
trans-
formerless (OTL) circuit and, therefore, deliver
the
output
signal with extremely small
distortion
compared with
that
of
the
conventional
power
