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c
generated
by a
local oscillator. This
mixer
converts
the carrier
frequency to the
10.71\,4H2 intermediate
frequency. Care{ul
attention
to its
thermal and
electrical characleristics
has minimized
drift,
thus
obviatinq
the necessity
for
AFC.
The 107[,4H2
converted
siqnal
is lhen
fed to a
phaselinear
ceramic
lF
Jilter,
followed by an
lC limiter. lt is
then,
in
t.rn,
processed
lhrouqh dn
FIVI
drqcrim;na_
1or. The
output
of the
Fl\4 discriminator
is fed to a
buffer
amplifier
which then
drives the demodula
tor,
IF STAGES
The
lF section
consists
of
four traosistors
and
sax
ceramic
filters. The
characteristics
o{ this
filter
are
ideai
in thal
the 200KHz
passband
is
phase
linear,
with
sharp
cut-of{
slopes.
lts exceplional
phase
lineariry ässures
the ellminalion
ol
ä malor source
o{
high'{requency
distorlion
and
a loss o{
stereo
separation.
The
sharp cutoff
slopes
provide im
proved
selectivity,
permitting
reception
of closely
spaced
channels,
LI I\4ITE R
The l\,4odel
2245 utilizes
multi-staqes
(transistor
plus
lam;ter
diode and
lC) limiter amplifier
with a
very small
dynamic
symmetrical
aperture,
elirni_
nating
the need
for AGC circuit
which introduces
low
{requency distortion.
Undesirable
Amplitude
Modulalion
(AM
signals, AN,4
noise, AI\4 dislortion)
are
removed
frorn the
1F
signal
wilhin the
limiter.
FIM STEREO
DEIV]ODULATOR
The composite
audio signal
{rom
the
bLrffer am-
plifier
is {ed inlo
the multiplex stereo
demodlllator
circuit consisting
of 11 transistors and 6
diodes.
lhe
l9lP1
pilot
siqaal conldin.d
in
Lhe
composrte
audio
signal is doubled
into 3BkHz after
two stage
amplification
and
then the 3BkHz signäl
is further
amplified
to the
level necessary
to drive the diode
switchinq
circuit. The composite
audio signal
is
split
into
the right
änd left channeis by the 38kHz
switch;ng
signal in
the diode matrix circuit.
The
right and
left channel audio
signals are
processed
in
the crossralk
cancellinq circuit
which L]tilizes com
plementary
configuration
with NPN and
PNP
transistors.
The audio
signals are then
{ed into the
selector
switch
anand the TAPE OUT
jacks
from
the low
päss
Jilters
for filtering undesired 19
and
3BkHz
components
and enritter
followers for low
impedance
oulput.
The stereo
demodulator circuit
has been designed
with the
d+emphasis
net\,vork to
provide
flal
frequency
response up to
15kHz.
One
hundred
percent
air'tight
coils and
filters
are
incorporated
in
the
stereo
demodulator circuit
for improved
slabilitv
and
reliabilitv with
good
stereo
separation
and
frequencv
response.
The multiplex
stereo
demodulator circuit
has been
provided
with an
automalic
slereo/monaural
switching
circuit.
The circuil
checks
the
input
siqnal
intensity
and aclivates
the stereo
demodula
tor circuit
and
the stereo indicator
lamp aulo-
matically
only
when the
inpul signal is
power{ul
enouqh
10
provide
good quality
stereo
reception.
When
the
input signal
strength is below the
threshold
level,
the FM stereo
broadcast is
process_
ed as
monaural
signal and
improved signal-to_noise
rätio is obtained
in this mode of operation.
IIIUTING CIRCUIT
ln rhp dbsence
ol dn FI\4 carrier, dll
f[4
recpivers
produce
a
peculiar
noise. The
mutinq
circuit
elirninates
this noise,
providinq
vou
with noise-free
tuning
from slation-to
station,
A muring circuil,
consistinq ol a two trdnsistor
noise amplifier
and a thre+transistor
{including
one FET) switching
circuit, has been incorporated
in the
lvlodel 2245. The muring circuit
perfectly
mutes out
all the interstation noise and also
complptely
mules oul thp side slope spurious
response
of
the
unit. The circuil has been designed
to minimize
annoying
"pop"
noise
for velvet
smooth
tune in and
tune out.
AM TUN ER
The Al\4 tuner
ponion
of the l\,4odel 2245 has been
provided
with a tuned
RF ämplifier incorporaling a
three-section
variable capacitor
for improved
spurious
response ratio,
The
ceramic
filter
utilized
in the Al\.4
lF
ampliJier
comes
with higher selectivity
and wider bandwidth
for interference
{ree hi{iAI\l reception.
Following the
A[,4 lF amplif ier, tl're
Al\,4
detector
recovers
the audio modulation
and
provides
this
signal
to the
selector switch.
The Al\4
tuner and lF amplifier are subjected
to
the
action of an effective aulomalic
volume
control
circuit
which
maintains constant the
level
of all
stations
in
the Al\,4 band.
SELECTOR
SWITCH
Your
l\,4odel 2245
has the cäpability to operate
from a
variety of
program
sources, e.9., AM or
FM
broadcasts,
tlrrntable
(PHoNoi,
tape recorders
(TAPE)
or
anv other source
capable of
providing
IOO
millivolts
output
level
(AUX).
The selector
switch
connects
the
inputs oJ the TONE amplifiers
c
12
17


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