Keying Control - Swann CUBIC ASTRO 102 BX Service Manual

OCUBIC
COMMUNICATIONS
S"AIII
DIVISION
+10.5V
RI22
• +-10.5V
CR 05
CW SHAPING
it takes for C12S
amount of delay is
+l0.5V
T O-",*-e
-T- LINE CONTROL
EXT.o-. . .- -....,
!Cu
INT.
on the input of the timer has ceased. The amount of time
to charge is determined
by
the setting of Rl44, . thus the
controllable. Should VOX not be desired,
the VOX/PTT switch connects a + voltage
to the timer input via R14) when in the
PTT position
KEYING CONTROL
When in the CW mode of operation,
the CW line is high, and i t, through RIOl
cw
O"'VR"IO",I. .
-H.
biases QIOl on, effectively reducing i ts
LINE
collector voltage and cutting off Ql02.
KEYING
This makes the collector voltage of Ql02
CONTROL
rise, and CRI02 conducts in turn, biasing QI03 to an ón condition. Thus its
collector, the key line, is at a low value, its normal, un-keyed condition.
Should either the EXT KEY or the KEY
contacts be closed, the junction of Rl04
and RI05 in the collector circuit of Ql02
is grounded, removing the voltage to CR-
102 and the base of Ql03 causin~e col-
lector voltage to Ql03 (and the key line)
to risee
In the USB or LSB modes, the CW line
is low, and QlOl does not conduct. PTT
operation is then exactly as described
abave for CW, but if VOX is selected, the
VOX circuit provides a voltage to RI03
which causes Ql02 to saturate, again re-
moving voltage from CRlO~ and so Ql03
ceases to conduct and the key line rises.
The key line, when high, causes CRIO) to conduct through RIO? and RIOa
biasing Ql04 on. The combination of RIO? and CIOl control the rise charac-
teristics of the keying waveform, while the falling
characteristics are controlled by the discharge of
CIOl through RIOS and the parallel combination of
the base-emitter junction of Qlo4 and RI09. Wh en
Ql04 conducts, its collector goes low, lowering the
base potentialof PNP transistor Ql05, and it sat-
urates, energizing the "T" line.
When the "T" line and key line are. bath high,
CRI05 and CRI06 are reverse biased, allowing QlOS to
conduct, and charge CI05 through R121. This time
constant determines how fast· the "T/S" line is al-
lowed to rise to full voltage. The "T/S" line sup-
plies bias to the drivers for the transmit mixer,
Zl02 on the exciter board, thus permitting generat-
ion of the transmitter signal.
For lower speed CW operation, it is desirable
to have a slower ("softer") attack and decay time on the CW note, so the op-
erator may switch cl06 in parallel with CI05, thus increasing the time con-
stant. High speed CW is more easily copiedwhen it has a fast ("hard") at-
tack time, so clo6 is then switched out of the circuit, at the operator's
option.
6-?