Although Q1
is
now off and Q2
is
on, the circuit
cannot remain in this inactive (quiescent) condi-
tion indefinitely because of the action of ca-
pacitor C20. This capacitor has previously been
charged to the Q2 collector voltage. Since the
Q2 collector voltage has very rapidly become
less negative C20 must now discharge. This
is
shown by the flat top line in Figure 10. The
discharge path
is
through control R21. The
time constant of the discharge curve
is
de-
termined by capacitor C20 and control R21. The
charging time of C20
is
very short with respect
to the discharge time. This
is
due to the high
resistance value of control R21 as compared
with resistor R20. As C20 discharges, the
voltage at the base of Q1 becomes less positive
(more negative).
When the conducting level of Q1
is
reached and
the transistor starts to conduct as shown at TI,
the complete cycle
is
now reversed, with Q1
conducting to saturation and turning off Q2. The
circuit then reaches its second inactive (quies-
cent) condition."Capacitor C1 having previously
been charged, now discharges at a time constant
determined by the value of C10 and control R11.
As long as the key lever
is
held in the dot posi-
tion, the dot generator multivibrator continues
to run free. Each stage
is
then alternately on
and off for relatively long periods (determined
by the values of C10 and R11, andC20 and R21),
followed by a very rapid switchover to the
opposite stage.
The collector output signals of Q1 and Q2 are
fed to other sections of the circuit. The output
from the collector of Q1
is
fed through R30 to
the base of Q3, and through R79 to the base of
Q7. The output
is
fed to Q3 to make the multi-
vibrator action self-completing. Once the mul-
tivibrator
is
started, any movement of the key
lever will not have any effect until the dot
and following space have been completed. The
operation of Q7 will be explained in the following
section.
Page 37
Driver Follower And Switch
The base of switch transistor Q8 draws more
current than can be supplied by the dot gen-
erator transistors. Therefore driver transistor
Q7
is
used as an emitter follower to supply the
necessary drive for Q8. Resistors R73, R74,
R75, R76, and R78 divide the power supply volt-
ages to set the proper bias voltages to fully
control Q7 and Q8.
Transistors Q7 and Q8 have a positive base bias
voltage which keeps them cut off (no current
flow). Each time the collector voltage of Q1
is
at -16 volts, transistor Q7
is
biased to
conduction. This action then biases Q8 to a
point where it will also conduct. The output
from Q7
is
fed through resistor Rlll tothe base
of audio clamp Q11. The operation of Q11 will
be explained later. The collector output of Q8
is
used to key the transmitter. This waveform
is
shown in Figure 12.
+1.S VOLTS
0 VOLTS
-0.2
VOLTS
TO
TI
T2 T3 74
TIME
SIGNAL AT BASE OF
Q8
Figure
12
Manual keying may be accomplished by con-
necting a hand key between the Hand Key and
Gnd terminals. This operates Q7 and Q8 inde-
pendently of the Keyer operation by shifting the
bias voltage on Q7. The Hand Key terminal
is
also grounded when the slide switch
is
placed
in the Hold position. This allows continuous
transmitter operation for tuning or adjustment
purposes.
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