rf - Free and Open Source Software

I
Telephone Beeper
The following is a description of a telephone
"beeper" to be used when recording
telephone conversations. The "beep" can be
adjusted to beep every nine seconds as
required by the Public Utilities Commission.
Without going into the legality of the
device, let's say it can be used to insert a
beep into the telephone conversation that is
being recorded, by inductively coupling into
the telephone coil. The use of the device is
visualized when recording phone patch traffic
or recording a telephone message to be
transmitted at some later time.
Theory
A 2N333 and 2N 1305 transistor forms a
multivibrator whose time of beep between
pulses can be adjusted by a 250K potentiometer.
The pulse stays on for one half
second, allowing it to drive a I kHz oscillator
much better than a saw tooth or
unii unction type will drive it. When the
pulse is too narrow ihe tone is not clear,
thus experimentally the multivibrator was
used.
Ed Marriner, W6BLZ
528 Colima Street
LaJolla, California 9203:
A brown bead No. 47 lamp bulb acts a'
the pilot light and also as a non-lineal
element which helps to sustain reliable
pulsing periods. The multivibrator drives ~
feedback type oscillator using a 2N 1306 as
the oscillator. This oscillator signal is arnpli
fied by a 2N1306 to create enough current
through a coil to generate enough of a field
to couple into the telephone instrument coil
Construction
The "beeper" is built into an LMB type
box, 3-1 /2" wide, 2" high and 6" long. FOJ
simplicity the parts are mounted on terminal
strips rather than on a printed circuit board.
Power is supplied from a 9 volt mercury
type battery for long life, although, any 9
volt battery should last a very long time. The
amplifier's source is 22 volts, which creates
more current through the coupling coil.
Many types of coupling coils were tried,
but an S53X output transformer seemed to
work the best. The case was pried off and
then the keeper or end of the core was
driven off, using a hammer and screw driver.
It was thought a stronger field could be
obtained by sawing off one of the sides of
the transformer to concentrate the field
between the center and one outside core,
but there was no difference in the coupled
signal and it was not worth the effort.
There are no special precautions in wiring
the unit except to get the polarity of the 15
mF condenser in the multivibrator circuit
correct. If it is backwards, the oscillator will
not work . An indication that the circuit is
functioning can be determined by watching
the lamp blink.
The spacing of the pulse can be 'set by
2'01(
VARY TO
SPACE PlA.SE
."
2.21( 120 K
210333 12 K
_ + 2.9 K
1 5 ~
..,
1
BROWN BE AD
2NI3O!l
Z10 K
0'
'"
BLOOPER TO BE USEO ~E N RECORDlNG
TELE~E CONVERSATIONS
2NI306
' "
.0'
2 N1 306
'"
UNIVERS.lU.
OUTPUT TRANSF
10K PRI
r=~
'" TRIAO S~3 X
+22 _6 9 :&
-"
Beeper to be used when recording telephone
conversations.
Note the battery mounting and parts insta
lled on terminals.
88 "7') lA 1\ r: 1\ 7111.I c: