A two-way Morse practice set

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Introduction

The first step to learning Morse is to be able to memorise the sounds of all letters and numbers. This can be accomplished with the help of Morse practice tapes or classes. Once you know all the characters, the WIA Morse practice broadcasts and/or continuous VHF Morse beacons can be used to increase your receiving speed.

Additional practice is best obtained by having Morse (CW) contacts on the HF bands. However, many use shyness as an excuse to not use Morse on the air. Others are restricted by their licence grade to VHF/UHF operation and/or may not possess HF equipment. For such people, this Morse practice set is the next best thing to actual CW operating because it allows you to have two-way Morse 'contacts' with a person in another room or even an adjoining property. The advantage of this sort of practice is that one learns operating skills and procedure as well as sending technique.

How it works

The system consists of a pair of Morse practice oscillators connected by a piece of two-conductor cable (Figure One). Pressing the key on one unit produces a sound in both units. The receiving station can interrupt the sending station at any time by pressing their key. This is just like the "break-in" CW facility provided in most modern HF transceivers and makes this project particularly suitable for already licensed amateurs wishing to brush up their operating technique for a forthcoming DXpedition or contest. No originality is claimed for the idea, which is described in Reference One.

Though two stations are shown here, additional sets can easily be wired in parallel. Such multi-station operation has a number of advantages. For example, it could allow a small class to have DX or net-style 'contacts' - thus simulating multi-operator or competitive operation. In such a situation, the classes' trainer could pretend to be a rare DX station calling CQ and students could compete with one another to make the first 'contact'.

Block diagram of Morse practice set

The oscillator/buzzer

You will notice that the block diagram specifies that either an oscillator or buzzer could be used as the sound making device. A system using buzzers is cheap and simple (buzzers being available off the shelf), but transistor oscillators produce a nicer sound and cope better with faster speeds.

Transistor oscillators are commercially available in kit form (see later) or can be built from scratch. The kit is perhaps best if you have to buy all parts new. However, those with deep junk boxes would save by using available components instead. The remainder of this article provides details of an oscillator that you can build at home. Even if you have to buy the Morse keys new, a two-station set should cost between thirty and forty dollars to duplicate.

Construction

Below is the circuit used in the prototype. Two 'stations' are shown, though more can be added if required. The oscillator in each station uses a standard 555 timer chip. As is apparent from the photograph, each oscillator is built on a piece of matrix board about 30-40 mm square. Vero-type strip board could be used instead, but component placement will be more difficult because of the need to solder components to the right tracks. The 0.1 uF capacitors are polyester or disc ceramic, while the 100 uF capacitors can be a tantalum or electrolytic. If you are on a tight budget, the speaker, battery snap and (possibly) some resistors and capacitors can be salvaged from a broken transistor radio - component values are not particularly critical.

A speaker of any size can be used. For economy and compactness, a size of 38 to 76 mm is recommended. You may care to add a headphone socket if you intend to use the oscillator to practice while not disturbing others. A socket with an in-built switch to silence the speaker when the headphones are plugged in is recommended.

Each station needs between 6 and 12 volts to operate. Nine volt batteries were used in the prototype. However, if you intend to use the set a lot, a bank of AA, C or D-sized cells in a battery holder will provide more economical operation. Because all units are 'master stations' with their own batteries, each unit can double as a stand-alone code practice oscillator when solitary practice is required. If this feature is desired, use two-conductor plugs and sockets (3.5 mm mono connectors are ideal) to allow the connecting cable to be easily disconnected.

Circuit of Morse practice set

Testing and operation

Check all oscillators individually before connecting them together. Pressing the key should produce a tone that is pleasant to listen to and of sufficient loudness. Vary the 10k and 270 ohm resistors to set pitch and volume respectively.

Once satisfied with the performance of each station as a stand-alone unit, wire all units together with two-conductor cable. As it is carrying only DC, the cable need not be shielded. The thin type used for wiring up hi-fi speakers is ideal.

Keying one station should activate all oscillators. If not, check that the polarity of the wires to each station is correct. Use enough wire to separate the stations far enough so that the operators can neither see nor hear one another, so that Morse becomes the sole medium of communication.

The system as presented here is fairly basic. However, various 'bells and whistles' can be added to make operating more comfortable, or more like real live CW operation.

For example, many operators become fatigued when subject to a tone of uniform pitch for long periods. Replacing the 10k resistor with a variable resistor (say 20 to 50k) allows the pitch of each oscillator to be set to the operator's taste.

To make practice sessions more like on-air operating, many things could be done. For example, a resistor in series with a station's key would reduce the loudness of that person's 'signal' in the other people's stations, thus simulating low power (QRP) transmission. If a means could be found to vary supply voltage to each station automatically (say from 4 to 12 volts), over a period of several minutes, signal fading (QSB) would be the result. These effects would of course be made even more realistic by using an audio mixer to introduce real interference (either man-made or natural) from either a continuous loop tape player, digital voice recorder or HF receiver. These embellishments are not necessary for the casual learner, but could be useful to test an operator's ability to pass messages under adverse receiving conditions.

The above ideas have not been tried by the author, but are merely proffered as examples of how a very simple project such as this can become as elaborate as the builder desires.

A note about keys and kits

While Morse can be sent on an improvised key made from a hacksaw blade or piece of tinplate, it is better to use a proper key. Keys can either be bought new or second hand. Dick Smith Electronics is getting out of kits, but you may still find a Funway 2 code practice oscillator, which includes a key (K-2623). Keys also show up at radio junk sales and hamfests.

Reference

1. Williams N, Rowe J Basic Electronics Sungravure 1979, p85

This article appeared in Amateur Radio April 1998 with only minor updates since.