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OCUBIC
COMMUNICATIONB
S""AIfI
DIVIBIDN
current limiting resistor Rl12 to the base
of QI03.
Q103 supplies a current
to
PIN
diode
CRlOI which
serves
as a
variabIe
attenuator,
thus
supplying
AGC
to
the
O
noise
blanker
receiver.
The Rl25 , Rl26,
Cl15 and Cl16
network
integrates all in-
coming signals
to drive UIOI and generate
AGC to prevent strong signals (SSB, AM, or
CW)
from generating cross modulation
in
the blanking gate.
The
bottom
half of TIOI
drives de-
tector CRI03, which supplies a
De
pulse to
the base of Q108 when a noise pulse is re-
ceived.
When QI08
is thus turned on, it
in turn causes PNP transistor QI09 to con-
duct, creating a blanking pulse across its
load resistor,
Rl34 ,
which is coupled to
the noise blanker gate in the I.F. circuit
on the exciter board.
+-NB
RI2B
BLANKER
AGC
RII2
PASSBAND TUNING INDICATOR
TlOI
HIV
PULSE
OUT
RI 7 0
en
UNE
RI . '
~UI07~}~
-
PULSE
DETECTOR 6
PULSE AMPLIFIER
PASSBANO TUNING INDICATOR
]11
C137~
A separate section of the front-panel
PASSBAND tuning control, RI03B, is used to
develop a signal
used to drive the series
of LEDs that
indicate
the status
of the
tuning
of the
passband circuit.
Rl66 is
used in series with it
to provide a range
calibration adjustment, and the output,
by-
passed by C138,
is coupled to
the analog
input
of
analog-to-digital
converter IC
ulo6, on the audio board.
ulo6 is capable of
free-standing op-
eration,
but to operate in such a manner,
it must be
provided
with an R-C
combin-
ation that sets the frequency of operation
of the internal
clock
oscillator on the
chip.
Rl68 and
C13? serve
this function.
The IC must also
be properly
initialized
when it is first powered up.
QI06 and its
associated circuitry perform this task. C-
139 charges
through
R16?
when
power is
first applied, thus allowing Q106 to
con-
duct until nearly full charge is achieved,
grounding the appropriate pins on the chip.
Once C139 has charged, Q109 ceases to con-
duct,
and the
initialization pins on the
IC are ungrounded, allowing it to operate.
When
power
is removed, CRl22 allows Cl39
to discharge rapidly.
The digitally-coded output of UlO? is
coupled to the
inputs of
PROM UlO?
The
internally stored code
in the PROM gener-
ates the
required
signals
to drive
the
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