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=] —> ieler4
@ Operation of FM Section
IF
PNS
LEVEL
]
DETECTOR
| MUTE
MPX
HIGH
CUT
CONTROL
SEPARATION
:
CONTROL
Reh
PNS
1C_ 20!
PAOOI3
OR
| LEVEL
circuit | peTeCToR | MUTE
ARC
Mark
Ill
MPX
1C 203
PAOOIS
Leh
HIGH
CUT
| SEPARATI on}
CONTROL
| CONTROL
Reh
ARC Mark V
The high-cut and separation, which were controlled by the
input signal strength level in the ARC Mark III, can also be
controlled by the noise level in the ARC Mark V. Therefore
noise
in strong signal areas, impossible to suppress before,
can now be suppressed adequately.
Noise Detector Circuit
Co-using the PNS HIGH
PASS
FILTER,
this operates by
detecting
the components
above
100 kHz
in the wave
detector output. The HPF output is amplified to a sufficient
level, rectified, phase reversed and then DC converted.
1.
Front end section
inemaaiadi i
Amp
Block
Gain
|/dB
MIX
Gain 10dB
=
IF Amp
Gain
|18dB
13dB
Cerami
21dB
ATT
ANT
RF Amp
RF
| Balun
—- Mixer
|
.
Filter:
IFT
| IF Amp
Filter
IF Amp
Filter
Tune
Volt
The
RF signal from
the antenna
passes through an atten-
uator constructed as a band-pass filter and is sent to the pi-
shaped
matching circuit, where high-end spurious response
is improved. The signal then goes to the next stage, the RF
amp. The RF amp employs a MOS FET capable of handling
a wide dynamic range. The output from the RF amp passes
through
a parallel
resonance
circuit,
is converted
to
a
balanced signal from an unbalanced
by a balun circuit and
then goes to the mixer stage. This is a J-FET single balance
ARC
Mark
V
Fig. 11
Input Level 35 dBuV Switch
The noise level ceases to control the high-cut and separation
when the input level drops below 35 dBuV, and control of
these
is carried
out
entirely by the input signai strength
level. This
is the same as in the Mark
III. This function
operates in this manner
because the noise level control will
always output a signal when the signal strength is below 35
dBuV, and signal strength control is sufficient for medium-
weak input signal areas.
Fig. 12
type mixer which can accommodate a wide dynamic range.
One of the IF signals from the mixer passes through the IF
amp and ceramic filters. Another IF signal goes to the AGC
amp.
This AGC
amp
can operate even
in the presence of
interference
signals. The AGC
amp
output
is fed back to
the RF attenuator circuit, forming a wide loop AGC. The
AGC
circuit
operates
at antenna
input levels above
65
+5 GB.
2. IF detector section
A single-tuning quadrature detection is performed by IC
PA0013
using IF amp
and T1 to obtain an audio fre-
quency output.
3. PNS section
This is a pulse noise canceller using IC PAO014 and CR
composite part CR1 which comprises filters.
4. Multiplexer section
Stereo multiplexing is performed by IC LA3376P. This IC
does not operate the stereo circuit in the absence of cur-
rent
flowing
through
the
stereo
indicator
terminal
(Pin 10).
5. Muting of weak incoming signals
IC PAOO13
develops
a DC voltage at pin 6 when
the
input is weak or detuned. When this voltage is applied to
pin 5 through
the filter consisting
of capacitors
and
resistors, the attenuator goes into operation. The on/off
(AUTO/MONO)
of this weak input signal muting is con-
trolled.
The
stop signal for the seek operation
uses a voltage
developed
at pin 6. (During
broadcast
reception,
the
voltage is at OV).
® Operation of AM Section
IC HA12434
used
in this unit is designed for electronic
tuning and provided
with
the output circuit of the stop
signals for seeking and VCO
buffer.
Its feature includes a
wide-band AGC.
1. RF amplifier section
This section performs a single-tuning 2-stage RF amplifi-
cation. The first stage is a narrow-band amplifier section
consisting
of
Q9
and
its load, i.e., resonance
circuit
(inductance
of
T2,
and capacitance of varicap diode
D8-1, C51).
The second stage is a section consisting of
RF amplifier
1 inside the IC and its load, or resonance
circuit
(inductance
of 174, and
capacitance
of D8-2,
C54). Pin 15 is not only a terminal lead to which the
load of RF amp 1 is connected, but also an input termi-
nal pin of the mixer input.
2. VCO section
The
VCO
(voltage-controlled
oscillator)
oscillates
at
its resonant frequency by the feedback circuit from pin
12 to pin 13 and the resonant circuit connected to pin
13. The resonant frequency is determined
by the induc-
tance of
L6
and the composite capacitance of Ca, Ca,
and D8-2.
Ca is a padding capacitor connected in series with capaci-
tance-varying varicap diode D8-3,
and Ca is a capacitor
connected in parallel with varicap diode depending on its
grade. All this contributes to better tracking with the RF
stage.
6. Local station seeking
While seeking strong signal stations, the gain of the front
end is decreased by making the voltage at AGC terminal
in the front end 4.5V by Q1.
7. Separation control, high frequency control.
Pin 8 of IC3 (LA3376P) functions as the separation con-
trol
(SNC)
pin, and
pins 7 function
as the
high-cut
control
(HCC)
pins. SNC
and
HCC
are controlled
by
the control
voltage from
pin 17 of 1C1 (PA0013). The
control
voltage can
be varied
by adjusting
semi-fixed
volume VR1, connected to pin 20 of IC1. SNC and HCC
are controlled
by the input signal strength
level. How-
ever, these are also controlled by the noise detector level
from
IC2
(PA0014,
PNS),
unless
the
input
signal
strength
is below 35 dBuV. The noise detector output
from pin 7 of CR1
is input to pin 16 of IC1. The noise
detector
control
of the high-cut
and
separation
will
switch on above 35 dBuV.
8. Mono/stereo
When
the
Mono
switch
is turned
on,
pin10 of IC3
(LA3376P)
will be opened, the stereo indicator will go
out,
and
the
output
will
switch
to monaural.
Pin
5
(MUTE
DRIVE
PIN) of IC1
(PA0013)
will also be
grounded, disengaging the level mute.
3. Mixer section
The VCO
output frequency from the VCO section and
the input signal from
RF amp 1 are mixed together at
the mixer
section to produce the IF component
(450
kHz).
4. IF section
The
intermediate
frequency
section consists of the
IF
filter (450 kHz) by T6 and CF2, the IF amp 1 and the
IF filter by T7.
Pin 8 is not only a load connecting
terminal
of the IF amp but also an input terminal
of
detector circuit 1.
5. Detector section
Pin
8 is connected
to the detector
and
provides
an
output
to pin 5, audio
output.
This
output
contains
both
audio frequency
component
(AC) and DC com-
ponent.
6. AGC section (AGC by the reception frequency)
The DC component of the detector output at pin 5 is de-
tected by AGC amp 1 at pin 1 by passing it through the
filter consisting of R55 and C73. The AGC starts operat-
ing at an input level close to the maximum
sensitivity.
The output of AGC amp 1 is connected to AGC amp 2,
and controls the gain of RF amp 1.
The
AGC
voltage
is developed
at pin 3 through
AGC
amp
3, and current flows through
D5 and D6, lower-
ing the impedance. As a result, attenuation is effected.
When
Q7
turns on and the load impedance of the drain
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