Pioneer H-2000 Service Manual page 7

H-2000
H-2001
1ST
IF
AMP
o3
FI!1
ANT
300s2
(Balanced
)
BAR
ANTENNA
o
FM Section
The
selected
FM
broadcast signal, received
at
the
antenna,
is
tuned
in
a
tuning circuit
consist-
ing
of
inductance
L
I
and
a
variable
capacitor;
after
amplification
in
RF
amplifier
Q
I
the
signal
is
passed
to
the next tuning circuit,
a
variable capacitor
and
inductance
L2.
In
these
two
stages,
the sensitivity
of
spurious
signals is
drastically
suppressed, so
as
to
improve
image
rejection
ratio
and
overall spurious rejection
ratio.
The
signal
is
then
inserted
to
mixer
amp-
lifier
Q2. This
signal
produce an
output
from
the
mixer which
is the
intermediate
frequency
signal.
This
IF
signal (10.7MH2) is
gained
through
IFT
T1
(intermediate frequency
trans-
former) and then amplified
by IF
amplifier
circuit
consisting
of I
transistor
and 1
IC.
The
IF
amplifier
includes
2
high-selectivity
ceramic
filters which afford
an
extremely
steep
cut
attenuation
of
frequencies outside the
IF
band,
and
guarantees selectivity
in
excess of
50dB between
signals, assuring
no possibility
of
interference from
adjacent broadcasting stations.
The
IF
amplifier
also
includes
limiting,
such
that
upon
reaching
a
certain value,
signals
are
not
further amplified, so that the output
is
constant. By virtue of
the limiter
effect,
the
capture
ratio
is
held
to not
more than
1.5,
and
interference between broadcasting
stations of
the
same
frequency
is
greatly reduced. Follow-
ing
the
IF
stages,
the
signal is detected
in
the
frequency discriminator
consisting
of
T2,
T3,
D3 and D4, from
which the
audio
frequency
modulation is
derived.
The recovered signal
is
decoded
by the
MPX (multiplex)
decoder
and
separated
into
stereo
right
and
left
channel
AN/I
IFT
T5
I\4PX
INDICATOR
cE
R
At\4 tC
FILTER
r4
Fis.
6
signals. The MPX circuit
employs
a
monolithic
IC,
ensuring
a high
level
of
performance
and
reliability.
o
About
the
PLL (Phase
Lock Loop)
This
unit
is adopting
in
its
MPX
circuit,
a
PLL
system, which utilizes no
coils and
capacitors
that
are changeable
of
their characteristics.
PLL
is
a
kind of
electronic
closed-loop
servo system
and
has
a
electronic control
device
to
detect
and
control
phase variations automatically. PLL
functionates
in
very
stable
to
the
specified
tolerance
and separation
factor
and
maintains
MPX
circuit in
constant condition.
o
AM
Section
The
selected
AM
broadcast signal received
at
the ferrite
bar antenna is mixed
with
the
local
oscillator
output (L6)
in
the mixer
amplifier
IC
1.
The
output of
this
stage,
the intermediate
frequency
signal,
is
passed to T4
which
consists
of
a
matching transformer and a ceramic
filter
of
high
sensitivity,
ensuring
good
band width
and
adequate
selectivity.
The
IF
signal
is
pro-
cessed
through 2
stages
of
amplification in
IC
I
which
are common
to
the FM section.
The
amplified
IF
signal then
passes
to
the
AM
detector
consisting
of T5
and D5
where
the
audio
signal component is recovered.
At
this
point the AGC
is
taken
off
and
feedback
through
a
network,
to
control
IC
1.
By
this
means
the
audio
level
is
maintained
constant,
against variations
of
antenna signal
strength.
RF AMP
o1
IV]IX
E R
a2
FM
IFT
T1
MPX CIRCUIT
AI\,1
DET
D5
FIVI
CERAIVIIC
FILTER
2ND,3RD IF
AMP
F2
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