T EVIS i - AmericanRadioHistory.Com

A TRANSISTOR
CODE PRACTICE
OSCILLATOR
Fig. 1. Truly "pocket -size' code
practice oscillator using transistors.
By
LOUIS E. GARNER, JR.
Cor:struction details on an extremely compact unit which
can be carried in a pocket and used, with privacy, anywhere.
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HE prospective amateur who must
learn the radiotelegraph code often
finds it difficult to work sufficient
"practice" periods into an already
heavy schedule. School, work. the
study of theory. and social obligations
may all combine to make the practice
periods erratic at best. On the other
hand, regular practice is essential to
developing reasonable skill --a moderate
period of practice repeated at frequent
intervals often is of more value
than long practice periods repeated
only occasionally.
One solution is to provide means of
practicing whenever the opportunity
presents itself -- during a lunch hour,
while in a waiting room, or whenever
a few minutes' spare time can be
found. Essential items are a code practice
oscillator, a headphone (or loudspeaker),
and a hand -key.
Unfortunately, code practice signal
sources which are normally available
are generally either too bulky or too
loud to be effective for this type of
40
practice. An electronic (vacuum tube)
code practice oscillator is likely to be
large and to require a source of power
which may not always be available;
a battery operated unit may have
short battery life and thus be prohibitively
expensive to operate. A buzzer
and battery combination is the least
expensive solution. but also the most
unsatisfactory. A buzzer not only requires
comparatively large amounts
of power, making it necessary to
either use large batteries or to replace
them frequently, but is also
likely to be too loud for practice at odd
moments it certainly would not be
satisfactory for use in a waiting room.
The ideal solution is a compact
oscillator using small batteries, with
long battery life, and supplying a
signal for earphone operation the
oscillator shown in Fig. 5 is a close
approach to this "ideal" unit. As can
be seen in Fig. 1, the oscillator is
small enough to slip in a coat pocket.
yet batteries are self -contained and
battery life is long. Ample power is
provided for earphone operation and.
under conditions of low ambient noise,
the earphone may be placed on the
table and heard by several persons.
On the other hand, the volume is not
so loud as to prove distracting to others
when the headphone is worn normally.
Construction of the oscillator should
not prove difficult, and the average
technician should be able to assemble
and wire the entire unit in a few
hours' time. The cost of the components
used, while not low, is still
not prohibitively high, and should be
well within the budget of the pro -
-pective "ham."
Circuit Description
Referring to the diagram given in
Fig. 3, a Raytheon 1"p-n -p" type)
CK722 transistor is connected as a
grounded -base audio oscillator. Feedback
is obtained by means of T,, a 1:3
interstage audio transformer.
The earphone and hand -key are
connected in series with the collector
circuit, and thus serve to open this
circuit when removed (or when the
key is open). Because of this, a single
s.p.s.t. switch is all that is necessary,
and this is provided in the emitter -
base circuit (S,).
Resistor P serves to limit current
drain and also has some control over
the frequency of operation.
Power is obtained from a penlight
cell (a). which supplies "bias," and
a small 15 -volt hearing aid type battery
(B,I v.'hich supplies collector voltage.
Construction Hints
No special precautions are required
when assembling and wiring the unit
shown and the builder need only follow
good construction practice. A
metal utility box, a plastic case, or
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