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Output is taken
to the
exciter
caoo
n211
CRIOO
CARRIER OSCLLATOR
I
Ral2
-C192
-=
Ra.07
R204
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_CUBIC
COMMUNICATIONS
SIIrAIfI
CIVIBION
CARRIER OSCILLATOR
to the base of
Ql20 is provided
by
the
~209-C231
network.
from the emitter of Ql21 through C232 and R212, and routed
board.
Since the ASTRO 102BX utilizes
only one
crystal filter,
the car-
rier oscillator frequency must
be
shifted appropriately when select-
ing USB,
LSB
or CW modes, so that
the
signal
will
fall
within the
pass band of the filter.
Only
one
oscillator is used,
with a crystal
switching scheme used to select the
proper crystal, depending
upon the
mode sel ected.
Q122 is
the oscillator,
with
bias
provided
by
R206
and R20?
Feedback is provided by C188 and C-
189.
R20S is the emitter resistor.
The collector load
is comprised of
TIOS and C18?,
which form a paral-
lel resonant circuit.
R204
and C-
190 form a decoupling network.
In the LSB mode,
a + voltage
is applied through
LI06 which for-
ward biases
diode CRI06, with R20S
serving as a ground return.
In this manner,
C196 effectively grounds the
lower end of
Cl94 and C19S,
placing YI03 into the circuit
between Ql22's
base and ground;
the oscillator then operates at YlOJv s frequency, as trim-
med
by
C19S.
At the same time,
the voltage drop
across R20S
reverse biases CRIO?,
preventing Yl04 from having any effect on the oscillator frequency.
In the
USB or CW receive modes, the
+
voltage is applied via LIO? to CRIO?, forward
biasing it
in the same manner as CRI06
in the LSB mode.
CRI06 is now re-
verse biased,
and Yl04
controls the frequency
of oscil1ation.
The exact
frequency is set
by
C19S.
When transmitting
in the
CW mode,
an offset is desired to place the
signal into the passband of the IF filter.
In the ASTRO 102BX,
this offset
is approximate1y SOO Hz from the receive condition, and is provided
by
"pul-
ling" the frequency
of Yl04.
In transmit,
the
CWX line is high,
forward
biasing CRIOS and reverse biasing CRI09.
C199 and C200 now affect the freq-
uency of n04,
and C199 is adjusted during alignment to provide the desired
frequency offset.
T
,
CW SIDETONE OSCILLATOR
When operating
in the CW mode,
a sidetone is
provided in the transc-
eiver's loudspeaker so that the operator may monitor his own sending.
This
signal is generated
by
CW sidetone oscillator UlOlB.
The frequency
of the
sidetone is determined
by
the
positive feedback path for UIOIB, that is, C-
106,
CIOS, and RllS.
The gain of the stage
is determined
by
the inverting
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