Akai AT-2650

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The
Quadrature
Detection
Circuit
is
comprised
of
a
Phase
Circuit,
a
Multiplier
Circuit
and
a
Low
Pass
Filter
(L.P.F.)
as
shown
in
Fig.
7.
There
are
two
types
of
Phase
Circuits,
the
Single
tuning
type
shown
in
Fig.
8
and
the
Double
tuning
type
shown
in
Fig.
9.
However,
because
with
the
double
tuning
type
there
is
less
frequency
deviation
in
relation
to
carrier
frequency,
linearity
is
improved
as
shown
in
Fig.
10
and
phase
distortion
is
reduced,
this
type
of
phase
circuit
is
employed
in
the
AT-2650.
Input
signal
S1
is
divided
into
the
part
which
enters
the
direct
multiplier
circuit
and
the
part
which
passes
the
phase
circuit
and
enters
the
multiplier
circuit.
The
signal
supplied
to
the
phase
circuit
is
always
90°
phase
delayed
at
L1.
Also
because
at
Non-modulation
time,
L2
is
tuned
to
10.7
MHz,
if
modulation
is
applied
and
$1
is
changed
from
10.7
MHz,
phase
deviation
at
L2
will
take
place
proportionately
in
relation
to
this
changed
part
and
this
becomes
S2
signal
which
is
delayed
in
relation
to
S1.
At
Non-modulation,
because
as
shown
in
Fig.
11,
the
input
signal
S]
and
90°
phase
delayed
(by
means
of
Ll)
signal
S2
are
switched
by
means
of
the
multiplier
circuit,
the
output
signal
becomes
S3.
Because
this
$3
passes
the
low
pass
filter
and
becomes
S4
fixed
direct
current,
the
detector
output
is
zero.
Then,
when
modulation
is
applied,
because
the
switched
output
is
varied
according
to
the
degree
of
modulation,
and
the
output
which
passed
the
low
pass
filter
becomes
the
pulsating
current
part
as
shown
in
Fig.
12,
detector
output
is
obtained.