Description
In
conventional
stereocoders,
encoding
is
performed
either
by
the
frequency-division
multiplex
method
(matrix method)
or
the
time—
division
multiplex
method
(switching
method)
using
a
switching
frequency
of 38 kHz.
Both
methods
entail
the
disadvantage
that
it
is
difficult
to
filter
out
system-inherent
unwanted
frequencies
in
order
to
achieve
high
channel
separation.
The
Stereocoder
GO
003
operates
in
the time-division
multiplex
mode
with
”soft“
switching
over
14
stages.
This
technique
produces
spurious
signals only
above
500
kHz,
which
can
easily
be
suppressed.
The
incoming
L
and
R
signals
are
applied
to
the
modulator
via two
identical
channels.
An
input
transformer,
an
18.5-kHz
Iowpass
filter
and
a
preemphasis
network
(which
can
be switched
off)
are
provided
in each
channel
as
well
as
a
switchable
level
attenuator.
Further
signals
in
the
range
between
53
kHz
and
about
100
kHz
(e.g.
traffic
radio,
SCA
channels)
can
be
added
without
affecting
Rear
view
GO 003
STEREOCODER
GO
003
the
multiplex
signal.
An
optional
SCA
modulator
can
be fitted
in the
Stereocoder
by removing
a
shorting plug.
The
modulator
consists
of
eight
electronic
switches.
After
adding
the
pilot
tone,
the
multiplex
signal
(MPX)
from
the
modulator
is
taken
to
both
output
amplifiers
via
a
Iowpass
filter.
It
is then
avail-
able
without
any
DC bias
at two
identical,
non—interactive
outputs.
The
pilot
and
carrier
frequencies
are
derived
from
a
4.256-MHz
crystal.
They
can
also
be
synchronized
to
an
external
19-kHz
frequency
by
means
of
a
built-in
phase
control
circuit.
For
mono
transmission,
the
signal
is
selected
from
the
L
or
R
channel
ahead
of the
modulator
and
then
directly
applied
to
the
output
amplifiers.
Except
for
the
power
supply,
the
entire
circuitry
of the
GO
003
is
contained
on
a
single
PC
board
which
is
easily
accessible
from
both
sides.
