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This circuit description is a brief summary of the
circuitry depicted in the block diagram on page 4.
For
more
complete
details, please
refer
to the
block diagram.
4.1 MAJOR
FUNCTIONS
The
F-9 is a PLL digital synthesized tuner re-
ferenced to a crystal oscillator.
Its main functions
are as follows:
1. Frequency Range
When
the AM
CHANNEL
STEP
switch is set
to the 10kHz position.
AM:
520kHz to 1610kHz in 10kHz step.
FM:
87.5MHz
to 108.0MHz
in 100kHz
step.
When the AM CHANNEL
STEP switch is set to
the 9kHz position.
AM:
522kHz to 1602kHz in 9kHz step.
FM:
87.5MHz
to 108.0MHz
in 50kHz step.
2. Tuning
e Tuning is by an UP or DOWN key. Pressing the
key once
changes
frequency
1 step (9kHz
or
10kHz
in the AM
band,
50kHz
or 100kHz
in
the FM band).
Holding the UP or DOWN key
depressed causes the frequency bands to be scan-
ned.
e Positioning
the
TUNING
MODE
switch
to
AUTO and pressing the UP or DOWN
key once
causes the unit to go into the auto search tuning
mode.
In this
mode, the unit automatically
scans
the frequency
band,
with scan stopping
at, and tuning into any broadcast station trans-
mitting a signal exceeding a prescribed level of
strength.
@ Pressing
the
STATION
CALL
key causes
the
unit to directly tune to a frequency preset into
the unit.
3. Memory
e Up to 6 FM and 6 AM frequencies can be preset
into the memory.
e A special memory
holds the frequency of the
station
tuned
at the time the power
supply is
cut OFF.
When power is restored to the unit,
tuning is automatically
made
to that station.
4. Indicators
e FM and AM band indicator.
@ FM STEREO reception indicator.
4.2 FM TUNER SECTION
FM Front End
The RF amp uses two newly developed D-MOS
FETs
with
improved
high-input
characteristics,
improving
both
intermodulation
interference
elimination and sensitivity.
These FETs operate in
a negative-phase mode, and are coupled in a push-
pull configuration.
The
mixer also uses a newly developed circuit
with
excellent
RF
mutual
modulation
charac-
teristic,
and a double
balanced mixer with an
FET constant-current buffer.
The
tuning circuit
consists of four twin-type
varicap
diodes,
also
with
superior
high-input
characteristics.
This
circuit
and
component
combination gives the F-9 interference elimination
performance
comparable
to
that
of a variable
capacitor
type
tuner,
and
attains
particularly
excellent RF intermodulation characteristics.
FM IF Amplifier
The FM IF circuit may be switched between a
WIDE
and NARROW
band range.
In the WIDE
mode,
better sound
quality is attained,
and the
NARROW
mode features better station selectivity.
Two
ceramic
filters
with
superior
group
delay
_ frequency
characteristics
are used in the circuit
during WIDE
mode
operations,
and two
narrow
band ceramic filters are inserted between the WIDE
stages during NARROW mode operations.
Darling-
ton differential limiter ICs are used between stages,
and the final stage uses an IF system IC (PA3007).
PA38007
not
only
features
better
characteristics
than previous IF system ICs, but also has a built-
in noise
muting (anti-hum)
circuit.
In the F-9,
only the IF limiter amp section of this IC is used
in the signal path, with the built-in FM detector
being placed in the control circuit.
Detection Circuit
The F-9 uses the digital method of detection.
The 10.7MHz IF signal is input into the convertor
IC (PA5001).
PA5001 includes a push-pull local
oscillator
circuit
and
a linear-multiplier
mixer
serving to beat down the 9.44MHz local signal to
1.26MHz.
FM detection is performed on the no.2
IF signal
(1.26MHz)
by the digital detector IC
(PA5002).
Since the FM signal is an inconsistent wave, it
can
be demodulated
after being converted
to a
DC level.
The IF signal is converted to a trigger
pulse by the differential circuit, and this pulse is
used to trigger the astable multivibrator function-
ing as the PPM
(pulse phase modulation)
signal
5
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