Automatic telegraph key. Scheme, description

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Automatic telegraph key

Radio - for beginners

For many years, radio amateurs-athletes and telegraph operators of communication centers for the transmission of Morse code prefer to use an automatic telegraph key. Such an electronic device, controlled by a mechanical manipulator, provides a clearer transmission of Morse code characters with less stress on the operator's fingers. It also allows you to easily adjust the speed of transmission of characters of the telegraphic alphabet, without violating the accepted ratio of the duration of the sounding of dots and dashes (1: 3).

We offer for practical use a simple automatic telegraph key on three microcircuits of the K155 series (Fig. 1).

Automatic telegraph key
Fig 1. Telegraph key

It contains a clock generator on the elements DD1.1-DD1.3, a shaper of "dots" and "dashes" on D-flip-flops DD3.1, DD3.2, a pulse adder on the element DD2.4, a tone generator on the elements DD2.1, DD2.2 and transistor VT1, which serves for auditory control of the transmission of a telegram, an amateur radio transmitter control unit (transistor VT2 and electromagnetic relay K1) and a manipulator SA1 with element DD2.3.

How does such a telegraph key work? In the neutral position of the SA1 manipulator, when its armature does not touch the side contacts, the clock generator does not work, as it is blocked by a low-level voltage at the lower input of the DD1.1 element according to the circuit, connected to a common wire through a resistor R3 of relatively low resistance. The control tone generator is also blocked by a low-level voltage from the output of element DD2.4. This element is in the zero state because at this time the direct output of the trigger DD3.1 and the inverted output of the trigger DD3.2 has a high voltage.

The operation of the telegraph key is illustrated by the time diagrams shown in fig. 2.

Automatic telegraph key
Rice. 2 Timing diagrams

To form a "dash", the armature of the SA1 manipulator touches the left (according to the diagram) contact. Element DD2.3 switches to a single state and a high-level output voltage starts the clock generator. From this moment on, the clock generator pulses appear at the output of the matching inverter DD1.4 (diagram a in Fig. 2), which are fed to the input C of the trigger DD3.1. The period of the pulse sequence of the clock generator, regulated by the variable resistor R1, is equal to the duration of the "point".

On the edge of the first pulse, the DD3.1 trigger switches to the opposite state, as a result of which a low-level voltage appears at its direct output, which translates the DD2.4 element into a single state. At the same time, the tone generator is turned on, since now a high-level voltage has appeared at the top input of the DD2.2 element. The audio frequency pulses are amplified by the transistor VT1, which is turned on by an emitter follower, and from the engine of the variable resistor R7, which is included in the emitter circuit of the transistor, the pulses are sent to the headphones BF1. At the same time, relay K1 will operate, contacts K1.1 of which manipulate the transmitter.

On the edge of the second pulse of the clock generator, the trigger DD3.1 switches to a single state and the voltage drop at the inverted output switches the trigger DD3.2 to the zero state (diagrams b and c in Fig. 2). Now, at the lower input of the DD2.4 element according to the circuit, there will be a low-level voltage, but the single state of this element will remain for the duration of the two "points" (diagram d in Fig. 2). Only at the front of the fourth pulse of the clock generator, when both triggers return to their original state, the DD2.4 element will go to the zero state and block the tone generator with a low-level output voltage. At the same moment, relay K1 will release the armature. There comes a pause, which is equal in duration to a "point", the next cycle of sign formation begins. The duration of each "dash" is three times longer than the "dot" period, which corresponds to the rules for transmitting the telegraphic alphabet.

To form "points", the armature of the manipulator SA1 is set to the right position. In this case, the DD2.3 element is again in a single state and starts the clock generator through the diode VD1. At the same time, a low-level voltage appears at the input R of the trigger DD3.2, as a result of which the trigger is locked in the zero state. The high-level voltage at the inverse output of this trigger will not prevent the pulses coming from the direct output of the trigger DD3.1 to act on the element DD2.4. At the output of this element, "dots" will be formed until the armature of the manipulator is set back to the neutral position.

What is the purpose of the diodes VD1-VD3? Diode VD1 is decoupling. When the DD2.3 element goes into a single state, a high-level voltage is supplied from its output through this diode to the lower input of the DD1.1 element, which starts the clock generator. This diode, in addition, prevents the low-level voltage from the DD2.3 element from entering the lower input of the DD1.1 element during those periods of time when the DD2.4 element is in a single state and the clock generator is in the generation mode with a high-level output voltage. Therefore, both "dots" and "dashes" will be formed completely, regardless of the moment the manipulator returns to the neutral position.

Diode VD2 also performs a decoupling function so that the low-level voltage at the output of element DD2.4 does not interfere with the operation of the clock generator.

Thanks to the VD3 diode, regardless of whether the armature of the manipulator is moved to the right or left position, the DD2.4 element will switch to a single state.

Diode VD4 shunts the winding of the electromagnetic relay K1 of the transmitter control unit. The fact is that at the time of the disappearance of the voltage on the collector of the transistor VT2 in the relay winding, which has a rather large inductance, a significant self-induction emf arises that can disable the transistor. The diode, by shunting the winding, protects the transistor from breakdown of its p-n-junctions. Inductor L1 and capacitor G3 form a rejection filter against the penetration of parasitic interference in those moments when the key works in conjunction with the transmitter.

Due to the inclusion of the transistor VT1 by the emitter follower, the resistance of the headphones BF1 does not really matter. Resistor R8 limits the collector current of the transistor in the event of an inadvertent short circuit of the emitter of the transistor to a common wire.

A drawing of the circuit board of the electronic part of the automatic telegraph key is shown in fig. 3.

Automatic telegraph key
Rice. 3 Wiring diagram

All fixed resistors type MLT-0,25, oxide capacitor C1-K50-6. Electromagnetic relay K1-RES55 (passport RS4.569.724). Choke L1 is wound on a ring with a diameter of 8 and a height of 4 mm from 600NN ferrite; it should contain 150-200 turns of PELSHO 0,25 wire.

If the telegraph key is not yet supposed to be used to work with the radio station transmitter, then the entire transmitter control unit, starting with resistor R8, can be excluded. In this form, the device will help the successful development of high-speed listening and transmission of the telegraph alphabet.

A possible design of the automatic telegraph key manipulator is shown in fig. four.

Automatic telegraph key

Automatic telegraph key
Rice. 4 Design of the manipulator

The base 1 of the manipulator is two plates of strong insulating material (for example, textolite) folded together, fastened at the corners with screws 9, 10. Anchor 2 is a plate 115 ... 120 long and 15 ... fiberglass. It is fixed with screws 18 between two metal corner posts 4 and is held in a neutral position by rectangular shock absorbers 3 made of foam rubber glued to the base.

On the corner posts 7 made of steel or brass, reinforced on the base with countersunk screws, there are adjusting screws 8, which form the fixed contacts of the manipulator. Against them, on both sides of the armature, solder contacts from the contact plates of an unusable electromagnetic relay, for example, MKU-48 or the like. After setting the necessary clearances between the armature and the side contacts, the adjusting screws are fixed with nuts 11.

The conductors connecting the circuit board with the manipulator are soldered to petals 5 placed under the corner posts.

See other articles Section Beginner radio amateur.

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Comments on the article:

Stephen
Good afternoon, to insert into the performance, you need a 20 second sound file (800-1000 Hz) with a telegraph key. Speed approximately 12-15 groups Tried from the air, a lot of noise. Please help Regards Stefan

UK8JBB, logger@inbox.ru
I liked to work on "vibra".

Alexander
This key has a drawback - if during the formation of a dash the manipulator is moved to the "dot" position, then the formation of the dash is interrupted and it turns out to be shortened. That is, until the transfer of the dash is completed, you cannot throw the manipulator to the "dot" position. Even at low speeds it is difficult to fulfill this condition, but at high speeds it is not at all.

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