3 - 2 TRANSMITTER CIRCUITS
3-
2 - 1 MIC AMPLIFIER CIRCUIT
Audio signals from
the
microphone are fed
to
the
limiter amplifier, consisting
of
0125-
0128,
which
has 6dB/Octave response between
300Hz and 3KHz.
The
output
of
the
limiter amplifier
is
similar
to
rectangular waves and includes harmonics.
These harmonics are eliminated by
the
low-pass filter
0129,
which cuts 3KHz
or
higher.
Filtered signals are fed
to
the
VCO
in
the
PLL board
to
make modulation.
3-
2 · 2 MULTIPLIER AND DRIVER CIRCUITS
The
VCO
oscillates a half
of
a transmitting frequency,
thus
the
multiplier
0208
and
0209,
multiplies it
two
times
to
obtain 156MHz* transmitting frequency.
This 156MHz* signal
is
fed
to
amplifiers
0211and0212
through band-pass filter L219, L220 and L221,
L222
to
obtain 200 milliwatts pure 156MHz* signal. While switching from receive
to
transmit,
0210
is
turned
ON
by the charged voltage of C269, until the charged voltage has been discharged, and this
function cuts the bias voltage
of
0211,...,
0213.
This prevents transmission
of
unwanted signals.
(*This frequency differs depending
on
the
version.)
3 · 2 · 3
POWER
AMPLIFIER CIRCUIT
The
output
signals from
0212
is
fed
to
the
power amplifier
0213,
and amplified
to
2.5 watts.
In
the transmit mode,
0216
and
0217
are turned ON, and
0217
makes L228 have high-impedance and
0216
feeds
the
signals
to
the antenna through the low-pass filter.
3 · 3 PLL CIRCUITS
3 · 3 - 1 LOCAL OSCILLATOR CIRCUIT
The crystal oscillator
0206
oscillates 35.77625MHz* with X202 for receive, 40.00125MHz* with X203
for transmit, and
the
signal
at
two
times this frequency
is
taken from
the
collector
of
0207,
and fed
to
the
mixer of the PLL circuit.
(*These frequencies differ depending on the version.)
In
the
receive mode, R+6V
is
applied
to
0210
through R223, L211 and R227, and
0210
is
turned
ON
and selects X202.
In
the
transmit mode, T +6V
is
applied
to
0211
through R224, L212 and R228, and 0211
is
turned
ON
and selects X203.
3 - 3 · 2 MIXER,
LOW-PASS
FILTER AND AMPLIFIER CIRCUITS
The
output
signals from
the
local oscillator circuit and the VCO signals fed through buffer amplifiers
0202
and
0203
are mixed by
the
mixer
0204.
The
output
signals are fed
to
the low-pass filter
to
filter
out
only the signals below 7MHz, then fed
to
0205
to
be
amplified
to
proper drive
level
(more than
3Vp-p)
of
the
programmable divider IC201.
3 · 3 · 3 PROGRAMMABLE DIVIDER CIRCUIT
The input signals
at
Pin 2
of
IC201 are divided by
the
BCD
input signals from the matrix board
at
Pin
3-14.
The programmable divider
is
also called the 1/N counter and the
BCD
value
is
N.
The relationship between the operating frequency and
the
divide number N
is:
N (divide number
of
programmable divider) =
Receive (or Transmit) Frequency
(MHz)
- Local Osc Frequency
(MHz)
_
1000
0.005
3-2
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