Revox B261

STUDtrR ]IEVOX
8261 SA
sEcTroN
3/4
STEREO DECODER
PCB I.726.760
DOUELE TUNED
19 kHz-CIRCUIT
76 kHz
OSCILNTOR
19 kHz BLOCKING
CIRCUIT
DEEMPHASIS
15
l5 kHz
LOW PASS
FILTER
The
38
kHz subcarrier
is
generated
in a PLL
from the
19 kHz
pj-1ot
tone. From
the 76
kHz oscillator, the signal
is
taken
through
a
pulse
shaper
to a
frequency divider
(:2).
The divided
38 kHz frequency
controLs the
MPX
switching
demodulator.
The
signal is taken through
a second
frequency divider
(:2)
to the
phase
comparator.
The
pilot
tone
is filtered
out of the
IUPX
srgnal in
a
wide-band,
phase-stable 19
kHz
band-pass
and also
taken to the
phase
comparator.
If the two
j-nput
signals
of the
phase
comparator do not
coincide with respect
to frequency
and
phase,
the
error
voltage
of this stage follows
up the
16 kHz
oscillator
through the loop
filter
and the
tuning
circuit.
The MPX
signal
is taken through a second
path to
the
19
kHz band
rejection
filter where the
piLot
tone
is
eliminated.
The signal
is now split
into the main channel through the
de-emphasis
network
and the auxiliary
channel through the
38 kIIz circuit.
For
stations
with weak reception, the SN ratio
can be
increased
at
the expense of cross
tal-k with the aid of
the SEPARATION
switch.
The
main channel
suppties
the'aggregate
signal through
an amplrfier.
The differential. signal
is developed
in the
switching
demodulator
from the auxiliary channel
and
taken to
the matrix.
After two
15 kHz low-passes
which suppress the
residual
MPX
si-gnals,
the
AF signals are input
to the audio
section.
The
pilot tone
is branched
off
in
the
first circuit
of the
19 kHz
band-pass
filter and
taken to a switching
demodulator
which operates
in
parallel
with the
phase
comparator.
The
subsequent
switching
stage
supplies the
pilot
present
signal
to the
microcomputer
control
unit.