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TECHNICAT
DESCRIPTION
GE NE RAL
Figure 10 is a block diagram of the Model 22358
Receiver showing the main functional elements
and input and output signal routing. Each AM
and FM front end has its own lF stages. For
clarity, only the left audio channel is shown; the
right audio channel is identical. The MONO
switch is common to both channels. All audio
controls are ganged to their counterparts in the
right channel, The left channel half of the front
panel DUBBING lN and DUBBING OUT jacks
are shown interconnected in this diagram. The
right channel of.each jack is wired to the same
circuit point in the right channel.
FM TUNER SECTION
FRONT END - FM antenna signals are applied
through a balun transformer to the antenna coil
which drives a f ield effect transistor R F amplif ier,
A four section tuning capacitor tunes antenna,
interstage and oscillator circuits which provide
exceptional selectivity and spurious signal re.lec-
tion. The signals from the amplifier are fed
through the double-tuned RF tank circuit to the
FET mixer stage, which is also fed by the signal
from the local oscillator. Careful attention to the
thermal and electrical characteristics of the oscil-
lator has minimized drift, thus obviating the
necessity for AFC. The 10.7 MHz converted
signal is then fed to the lF amplifier.
lF STAGES - The lF section consists of six
transistors and three stages of dual element
ceratnic filters. The characteristics of these filters
are ideal in that the 200 kHz passband is phase
linear, with sharp cutoff slopes. This exceptional
phase linearity assures the elimination of a major
source of high-frequency distortion and a loss of
stereo separation. The sharp cutoff slopes provide
improved selectivity, permitting reception of
closely spaced channels.
The Model 22358 utilizes svmmetrical diode
limiter circuits consisting of high-performance
Gold Bond Hot Carrier type diodes and lF limiter
amplifier with a very small dynamic symmetrical
aperture, eliminating the need for an AGC circuit
which introduces low frequency distortion. Un-
desirable Amplitude Modulation (AM signals, AM
noise. AM distortion) are removed from the lF
signa I with the limiter.
STEREO DEMODULATOR
The stereo composite signal obtained from the
buffer amplifier is fed to the FET muting circuit,
the FM OUADRADIAL OUTPUT jack and the
phase locked loop stereo demodulator lC circuit
where it is decoded into both left and right
channel signals. Each left and right channel signal
is then applied to the 19 kHz low pass filter
(LPF) and de-emphasis networks to remove the
undesired switching carrier signal in the audio
signals. Next, each audio signal is applied to an
audio amplifier consisting of NPN-PNP direct-
coupled transistor feedback pairs and amplified to
the required signal of about 755 mV RMS.
Finally, each amplified signal is fed to the
SELECTOR switch.
The phase locked loop lC in ihe multiplex stereo
demodulator circuit is equipped with a separate
automatic Stereo/Monaural switching circuit. The
circuit examines the input signal intensity and
actuates the stereo demodulator and stereo indi-
cator lamp automatically when the input signal is
of sufficient strength to provide high quality
stereo reception. When the input signal intensitv
is insufficient for this purpose, the stereo signal is
automatically changed to a monaural signal to
ensure quality reception and a high signal-to-noise
ratio.
MUT I NG CI RCUI T
In the absence of an FM carrier. all FM receivers
produce interstation noise. The muting circuit
eliminates this noise, providing noise-free tuning
from station to station.
A muting circuit consisting of a two transistor
noise amplifier and a three transistor (including
one FET) switching circuit, has been incorporated
in the Model 22358. The muting circuit perfectly
mutes out all the interstation noise and also
completely mutes out the side slope spurious
response of the unit. The circuit has been
designed to minimize annoying switching noise as
the tuninq band is scanned.
AM TUNER SECTION
The AM tuner section of the Model 22358 is
composed of one lC (incorporating an RF ampli-
f ier, local oscillator, mixer, lF amplif ier and
detector) and three transistors. One of them is a
signal strength indication amplifier, while the
other two are used for amplifying detected audio
signals. A three section variable capacitor is used
to insert two tuned circuits into the RF stage for
high selectivity and improved spurious signal
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