Page 40
At this instant both Q1 and Q5 are on and a
space results. This completes a dash and a
space at the collector
of
Q8 to key the trans-
mitter. This waveform
is
shown in Figure 18.
As the key lever
is
moved to the center or dot
position, clamp Q2
is
turned on and applies a
positive bias voltage to Q4. This voltage turns
Q4 off and Q5 on to set the flip-flop multivi-
brator. Thus, it
is
ready to start a dash the
next time the key lever
is
moved to the dash
position.
MONITOR CIRCUIT
Audio
Clamp
Each time Q7
is
turned on by a dot or dash
signal, a negative bias voltage
is
applied through
Rlll to the base of audio clamp Q11. This in
turn starts the free running audio multivibrator.
The audio multivibrator consists of transistors
Q9, Q10, and their associated circuitry. It
is
identical to the dot generator multivibrator, ex-
cept for component values. Both of these multi-
vibrator circuits work in the same way. The
any
difference being the audio multivibrator
-oscillates at an audio rate. This rate
is
de-
termined by the time constant of resistors R90
and R100, with capacitors C90 and C100.
0 VOLTS
-100 VOLTS
(MAX-105)
TO T1 T2
T3
T4
TIME
Q8
COLLECTOR OUTPUT TO TRANSMITTER
Figure
18
The output signals from the collectors of Q9 and
Q10 are fed to the primary winding of audio out-
put transformer T2. Capacitor ClOl prevents
any
DC
voltage from reaching the transformer.
The signal from the secondary winding of T2
is
connected across volume control R102. The
wiper of the volume control
is
connected to the
speaker. The control may be adjusted for the
desired listening level.
If
desired, the receiver output may be con-
nected between
GND
and the Receiver Audio
terminals.
This allows the audio to be heard in
headphones connected to the Phone jack of the
Electronic Keyer. The speaker of theElectronic
Keyer cannot
be
used when
a
receiver
is
con-
nected, as
it
is
of too high an impedance and
cannot handle the output level of the receiver.
If
speaker operation
is
desired, the individual
speakers of the Electronic Keyer and the re-
ceiver must be used.
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