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3. BLOCK
DIAGRAM
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FM FRONT
ENO
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ANTENNA
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TUNE
TUNE
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Flrormine
APC
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apitenna!
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AM TUNER —
4. CIRCUIT
DESCRIPTIONS
4.1
SIGNAL CIRCUIT
FM Front-end
The
FM
front-end
of this set uses a precision
frequency-linear
type
5-ganged
tuning capacitor.
The
circuit is shown
in Fig.
4-1.
The
antenna
input
is made
an
unbalanced
(752)
by an M-
coupled single-tuned circuit. The RF stage uses two
dual-gate MOS FETs (Q,, Q,) having superior high-
frequency
characteristics.
The
interstage
tuning
circuits are C-coupled double-tuned
for improved
reception.
The
phase
characteristic,
spurious
interference
ratio,
and
IF interference
ratio are
especially
good.
A dual-gate
MOS
FET
(Q;) is
also used at the mixer stage. The received signal is
applied to gate 1 and the local oscillator signal is
input at gate 2. The converted output (10.7MHz)
is taken
from
the
drain and applied to the IF
amplifier thru an IFT. The local oscillator (Q,) is
modified
Clapp circuit.
Its output is fed to the
mixer.
D, of the local oscillator is a vari-cap diode that
forms
part of the tuning capacitance.
A vari-cap
diode
is an element
whose
capacitance
can
be
controlled
by means of the impressed voltage, and
is designed to control the voltage relative to local
oscillator frequency deviation to within +100kHz.
This
control voltage is obtained
from
an APC
LOCAL
osc
(vco)
FM
IF
AMP
poe
roe
ir DIODE
H SWITCH
ii
TUNING
KNOB
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Q
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SENSOR
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SENSOR GAIN
BUFFER
AMP
------------
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ie;
=
(Automatic
Phase
Control) circuit. (See the de-
scription of the APC circuit on page 7.)
IF Amplifier
This tuner employs a dual IF amplifier consist-
ing of a wide band IF amplifier designed for high
separation,
low
distortion
reproduction,
and
a
narrow
band
IF
amplifier used for rejection
of
interference signals (Fig. 4-2).
The wide band IF amplifier has been designed
with the minimum
number of frequency selective
elements,
with
emphasis
being placed
on linear
phase characteristics. The narrow band IF amplifier
on the other band, has been
designed
with em-
phasis on selectivity. When the selector switch is
in the wide position, the signal path is FM front-
end > Q, > F, > Q,> T, > Ds, Ds > PA8001-A,
while in the narrow
position it is FM front-end
> Q, > F, > Q, > T, > D, > narrow IF amp. D,>
PA38001-A.
The
changeover
between
wide
and
narrow is performed of diode switches (D, to D,).
When
the selector switch is in the wide position,
D, and D, are biased in the forward direction and
D, and D, are biased in the reverse direction, thus
bypassing
the
narrow
IF
amplifier.
When
the
selector switch is in the narrow position, D, and
D,-are forward
biased and D, and Dg, are reverse
biased.
INDICATOR
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FUNCTION
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75Q
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Sat
FM
STEREO
DEMODULATOR
(PAIOOI -
MPX
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ears
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CERAMIC
FILTER
IF
AMP
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FILTER
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IF BAND
APC
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VOLTAGE
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recririen|
CONSTANT
VOLTAGE
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FIXED
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OUTPUT
LEVEL
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sanikate
Aon
Dx5
MULTI PATH
avs
POWER
SUPPLY
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FUNCTION
INDICATOR
BUFFER
AMP
ee
osc
to
APC
CIRCUIT
Fig. 4-1
FM front-end
Q7
Fig. 4-2
FM IF amplifier
: "ae van: CAP
towe R
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IF AMP
—
AGC
from
f CIRCUIT
NARROW
O
O
WIDE
\F
BAND
+B
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