Table of Contents
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| CRF-230B
1-3
TECHNICAL
FEATURES
The SONY
Model CRF-230B
is a high-perform-
aruc: radio receiver having many
features found in
cOmrmunication
receivers.
Among
them
are
the
fo lbwing:
e
4 total of 23 bands covering the broadcast fre-
quencies of any country in the world.
Included
we 2 fm bands,
19 sw bands,
a mw
band and
alw band.
e
(ET (Field Effect Transistor)
front ends in fm
and sw
bands provide superior sensitivity, image
rejection, and stability.
e
fasy-to-tune
sw
bands
due to a dual-conversion
system providing a uniform 600 kHz tuning range
on each band.
e
?roduct detector for receiving ssb signals.
e
An fm i-f circuit employing ceramic filters.
An
am
i-f circuit
employing
two
ceramic
filters
with two-step adjustable selectivity.
e
Individual
tuning
knobs
for
sw2~
19
bands,
swl/mw/lw
bands
and fm bands.
Preset-tuning
of three stations is available.
e
The
power
supply
will operate
from
household
current in any country of the world (via built-in
voltage selector), internal battery, or car battery.
e
Stable, noise-free
fm tuning by means
of AFC
and a muting system.
e
ANL
(Automatic
Noise
Limiter)
to
minimize
noise.
e
Up to 4 watts of undistorted audio power output
with two
built-in speakers
or external
speakers.
TO MUTING
CIRCUIT
1-4.
CIRCUIT
EXPLANATIONS
AFC (Automatic Frequency Control)
Available for Both FM Bands
In the
Model
CRF-230B,
the local
oscillator
frequency is above the signal frequency for the FM2
band, but below
the signal frequency for the FM1
band.
Because
of this, oscillator drift produces
a
detector
dc
output-voltage
change
of
different
polarity
on the FM1
band than on the FM2
band.
Therefore,
dc control voltages taken
directly
from
the detector output can not be used to stabilize the
frequency of the local oscillator.
To get around this
problem, a comparator circuit with selectable output
polarity is used (Fig. 1-2).
The detector output is
devided
by equal-value
resistors R232
and
R233
to
provide
two
voltages
identical
in magnitude
but
opposite
in polarity.
These voltages are
compared
against a reference voltage of approximately 1.5 volts
produced by the forward voltage drop across D204
and D205.
The resultant voltages are applied to the
bases
of transistor
Q211
and
Q212.
The
each
collector
voltage is fed through
AFC
switch
$202
to variable-capacitance
diode
(DO1
for FM1
band
and D101
for FM2 band).
The variable-capacitance
diode
is voltage
sensitive,
so its capacitance
(and
hence the oscillator frequency) depends on the mag-
nitude of the control voltage.
Load resistors R254,
R255
and
also
R258,
R259
are
connected
in a
balanced
bridge
and
the contact
voltage
at the
junction of R260 and R261
is used as a fixed bias
voltage
(0.7V)
for
the
variable-capacitance
diode
when AFC switch S202 is set to OFF.
IF T204 nee a
ie
c circa (DIO!)
TO AFC
CIRCUIT (DON
Fig. 1-2
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