Instruction manual
FRONT
END
FM
antenna
signals are applied
through
a balun
transformer
and
the
antenna
attenuator
switch to
the
antenna
coil which drives a field-effect transis-
tor
RF amplifier. When
the
ATTENUATOR
push-
switch is placed in
the
"OUT"
position,
the
attenu-
ator
circuit
is
cut
off
and FM signals are directly
fed
to
the
FM
antenna
coil. With
ATTENUATOR
switch placed in
the
"IN"
position,
the
signals are
attenuated
about
20dB by
the
attenuator circuit,
then
fed
to
the
antenna
coil.
The
amplified signals
from
the
RF ampl ifier are fed
through
the
triple-
tuned
RF filter
circuit
to
the
FET
Mixer stage,
which also receives
the
signal generated by
the
lo-
cal oscillator. This mixer converts
the
carrier frequ-
ency to
the
10.7 MHz
intermediate
frequency. Care-
ful
attention
to
its thermal and electrical characte-
ristics has minimized drift,
thus
obviating
the
neces-
sity for AFC.
The
10.7
IVI
Hz
converted
signal is
then
fed
to
a phaselinear ceramic I F filter, followed by
an IC limiter. It is
then,
in
turn,
processed
through
an FM
discriminator
.
The
output
of
the
FM dis-
criminator
is fed
to
a
composite
signal amplifier
which
then
drives
the
demodulator.
FM IF AMPLIFIER
The
IF amplifier consists of 8 ceramic filters and 7
stages
of
I F amplifiers including limiter stages.
The
characteristics
of
these
ceramic filters
are
ideal in
that
the
200KHz
passband
and
phase linearity as-
sures
the
elimination
of
a
major
source
of
high fre-
quency
distortion
and
loss
of
stereo
separation.
The
sharp
cut-off
slopes improve selectivity,
permitting
reception
of
closely spaced channels.
The
Model
2270
utilizes symmetrical
diode
limiter cir-
cu its
cons
isting
of
high
performance
Gold Bond
diodes and IC limiter amplifier with a very small
dynamic
aperture.
Thus, undesirable
Amplitude
Modulation is removed from
the
I F signal within
the
limiter
and
good
capture
ratio is also assured.
The
amplified
and
symmetrically limited FM sig-
nalsarefed
to
the
super-linear
discriminator
circuit
.
The
detected
audio signals are,
then,
distr
ibuted
to
the
QUADRADIAL jack,
MPXDecordercircuit
and
Noise Amplifier.
MULTIPATH INDICATOR
The
Multipath Indicator
circuit
is provided
to
aid
you
to
find
the
optimum
antenna
direction
for
a
desired
station.
Undesirable
Amplitude
Modulation
resulting
from
multipath
reception is
detected
and
displayed on
the
multipath
meter
when
the
MUL-
TIPATH pushswitch is held
"in"
. By
orientating
the
antenna
for
minimum
meter
deflection,
minimum
multipath
condition
is
obtained.
The
audible
signals
detected
are also fed
to
the
Tone
Amplifier
through
the
MULTIPATH switch, balance and
volume
con-
trol and
the
d
istorted
sound
due
to
the
undesirable
Amplitude
Modulation or
the
buzz-sound which are
proportional
to
the
MULTIPATH
meter
deflection,
can be heard
through
the
loudspeakers.
FM
STEREO
DEMODULATOR
The
composite
aud
io signal from
the
composite
signal amplifier is fed
into
the
multiplex
stereo
demodulator
circuit
consisting
of
11 transistors
and
6 diodes.
The
19KHz
pilot
signal
contained
in
the
composite
audio signal is
doubled
into
38KHz
after
two
-stage amplification and
then
the
38KHz
signal is
further
amplified to
the
level
necessary to dr ive
the
diode
switching circuit.
The
composite
audio
signal is
decoded
into
the
right
and left channels by
the
38KHz
switching signal
in
the
diode
matrix
circuit.
The
right and left
channel audio signals are processed in
the
crosstalk
cancelling
circuit
which utilizes
complementary
configuration
with
NPN and PNP transistors.
The
audio signals are
then
fed
into
the
selector switch
and
the
RECORD jacks
from
the
low-pass filters
for filtering undesired 19-and
38KHz
components
and
emitter
followers
for
low impedance
output
.
The
stereo
demodulator
circuit
has been designed
with
the
de-emphasis
network
to provide flat
frequency
response up
to
15KHz
One
hundred
percent
air-tight coils
and
filters are
incorporated
in
the
stereo
demodulator
circuit
for
improved
stability and reliability with good stereo separation
and frequency response.
The
multiplex stereo
demodulator
circuit
has
been provided with an
automat
ic
stereo/monaural
switching circuit.
The
circuit
checks
the
input
signal intensity and activates
the
stereo
demo-
dulator
circuit
and
the
stereo
indicator
lamp
automatically
only
when
the
input
signal is power-
ful enough
to
provide good
quality
stereo
recep-
tion
. When
the
input
signal strength is below
the
threshold
level,
the
FM
stereo
broadcast
is processed
as monaural signal and improved signal-to -noise
ratio is
obtained
in
this
mode
of
operation
.
MUTING
CIRCUIT
In
the
absence
of
an FM carrier, all FM receivers
produce
a peculiar noise.
The
muting
circuit
elimi-
nates
this
no ise, providing
you
with noise-free
tun
-
ing
from
station
to
station
. A
muting
circuit, con-
sisting
of
all
semi-conductor
switching
circuit
inclu-
ding
two
EFTs, has
been
incorporated
in
the
Model
2270.
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
11