Akai AM-2650

.
STEREO
DEMODULATION
CIRCUIT
As
shown
in
Fig.
14
for
FM
broadcasts,
the
sum
signal
(L+R)
consists
of
left
signal
(L)
and
right
signal
(R)
and
the
audio
frequency
band
of
this
signal
in
its
original
form
is
frequency
modulated.
On
the
other
hand,
the
difference
signal
of
both
(L—R)
is
changed
to
high
frequency
through
the
use
of
the
sub
carrier,
and
is
referred
to
as
the
sub
channel
signal.
The
carrier
is
further
frequency
modulated
and
sent
to
the
FM
stereo
transmitter.
es
os
5
eS
SSS
SS
Accordingly, for composite stereo signal demodu-
lation, the sub carrier used for demodulation at the
transmitter must be the same uniform 38 kHz signal
as the frequency and phase. If the 38 kHz waveform
is asymmetrical, channel separation will become poor,
At the PLL employed MPX stereo demodulator
circuit, as shown in Fig. 13 first a 76 kHz signal is
oscillated and when this passes the divider, a sym-
metrical 38 kHz signal is obtained.
COMPOSITE STEREO o
SIGNAL.
MAIN CHANNEL SIGNAL
+
SUB CHANNEL SIGNAL
MAIN CHANNEL SIGNAL
SEPARATION ADJUSTMENT
Fig. 15 MPX IC Function
L+R
SUB CHANNEL SIGNAL
38KHz SUB-CARRIER
LEFT CHANNEL SIGNAL
RIGHT CHANNEL SIGNAL
Fig. 16 Multiplex Decoder
1
2