Breaking into the Amateur Game

Radio Record, Volume IV, Issue 25, 2 January 1931, Page 7

Breaking into the Amateur Game

The Operator’s Exam.

a 41] HIS article, in continuation of %))i the series on "Amateur A Transmitting," deals with the \|- Amateur Operators’ Hxamination. Before a license to transmit is issued, the applicant must obtain a Government Amateur Operators’ Certificate; which is given after the examination has been passed. This is the most important part of getting a station-on the air, but there is nothing very difficult about it. For the average listener, with little or no knowledge of the Morse code, there is a certain ‘mount of patience required for the ssing of the examination. It usually takes a person with average spare time bout two months to prepare for it, but it is an interesting, pleasant occupation, and, as already mentioned, will reveal to the listener another side. of radio which before was but a meaningless jumble. Hence in any case it is well worth while to learn the code, for besides being used to a large extent by amateurs, it is the basis of communication between ship, shore and many commercial stations. Learning Morse. "THE examination is divided into two sections+-Morse and a written paper. The Morse part, in which candidates have the greater difficulty, will be dealt with first. In this a speed of ten words per minute, both sending and receiving, is required, each word being assumed to have five letters. This is a comparatively slow speed, but in the actual examination mistakes are not allowed, so it is safer to attain a speed of .18 or 14 words per minute before sitting. The test is given for about three or four minutes, the Morse being sent by a P. and T. officer through headphones, and in plain language, though numerals may be included. It must be copied down in pencil exactly as sent, while the sending required is simply a reversal of this process. Reeeiving Morse is generally considered by the beginner to be much harder than sending, but as we shall see later the standard of an operator is determined largely by his style of ‘sending, or "fist." It is best, however, to break well into receiving before starting on ‘sending. Now. the first step in learning the code -(a diagram of which is shown), is to ee the corresponding letters and bols thoroughly. It is essential to pi this by learning the symbols as ‘ty actually sound in practice-learn R as "dit-darr-dit," not "dot-dash-dot," and understand "dit-darr" as A, ete. This must be practised and the alpha‘bet and figures mastered’ so that their ‘sounds can be repeated quickly in or‘der. Then have them asked in any ‘order, until each can be given in the ‘"dit-darr" fashion without any hesitation. After this point it is only a matter of practice to gain speed in receiving, and a start may be made.on sending. For this a key and buzzer with a small battery, must be procured. As-the key may be used later on in a transmitter, it should be of sound construction, and its spring tension and contacts adjusted. for easiest sending. The knob of the key should not be grasped, but just pressed firmly by the first and second

fingers with a wrist action. The fingers must not leave the knob, and the muscles should be loose for steady, regular sending. The difference between a good and a bad sender depends mainly on the even spacing of the dots, dashes, and letters. A dot is simply a tap of the key knob, while the length of the dash is equal to three dots, and the time between parts of the same letter equals one dot. This spacing should be kept almost invariable, the speed of the morse being varied by the length of the spaces left between letters. The alphabet and numerals should be sounded on the buzzer at a slow even rate, but no speeding should be attempted until more practice has been had in receiving well-sent signals.. A learner’s "fist" will thus be considerably bettered. It is a good plan for two persons to learn the code together, so that each may give the other this receiving practice. The morse should be sent slightly faster than it can be received, and the letters, not the dots and dashes, should be written down, Any amount of practice may be obtained by listening to amateurs on the 7585 metre band, as special slow morse transmissions for beginners are given regularly. .At other times a slow but even sender may be chosen to copy.

Even though the speed permits of only a letter here and there being written down at first, soon calls and short words will come, and later with practice the missing letters will disappear. Perseverance is the keynote in learning the code. Speed is bound to come with practice. If now the learner returns to sending; he should have a good idea of spacing, and will probably ‘realise the value of a decent "fist." He should aim at slow, well-spaced sending rather than fast, jerky sending, readability coming before speed. To obtain an idea of relative speeds, clock tests may be made with any 20 words of five letters each, and these sent in just two minutes, the speed being then ten words per minute. If the learner becomes accustomed to copying morse

in legible writing at a little above this speed, no trouble should be had in passing the code examination, even though nervousness is experienced, as is often the case. The Written Examination. HAVING dealt with the harder part of the examination, we now come to the second part, the written paper. The requirements here are not highly technical. All that is necessary is a knowledge of simple short-wave transmitters and receivers, elementary electrical principles, and the Government, amateur radio regulations. Usually the paper consists of about 15 questions, divided into 4 on the regulations and 11 on the rest. Of these a choice of 10 is given, 3 on the regulations tions, divided into 4 on the regulations and 7 on the rest. The time allowed is 3 hours, and the pass standard required about 50 per cent. A great deal of information which is necessary for the examination is contained in the "Radio Listener’s Guide,’ and if this has been read thoroughly, especially the glossary, the exam. will be much easier. A candidate should be able to draw a circuit diagram of the complete transmitter, including the power supply he expects to use. This is a very frequent

question, and an easy one, as will be shown in the next article. The circuit of the transmitter is much simpler than that of the average receiver, while every amateur constructor is familiar with the two chief types of power supplybatteries and valve, or chemical rectified alternating current (R.A.C.). The parts used in a transmitter are much the same as those in a receiver, and their use and operation should be known, as such questions as "Hxplain the use of the radio-frequency choke, and the grid-leak, in a transmitter," are often asked. In the majority of transmitters there is a single valve which is simply an oscillator. Also, as with regenerative receivers, there are two general types of transmitting circuits-those using in-

ductive coupling feed-back from the plate to the grid, and those using capacitative coupling. The elementary theory of how the valve oscillates should thus be known. Further descriptions of transmitting circuits and parts will be given in the next article. fo Typical Questions. A QUESTION often asked is how the power input tu the valve would be measured. ‘The input, which is mea sured in watts, is simply the voltage on: the plate of the valve (corresponding to the voltage of the "B" battery in a receiver) multiplied by the current in amperes drawn by the plate. These would be measured by means of a voltmeter connected across the plate power supply, and a milliammeter in the positive lead to the plate. Thus, if the plate voltage is 200 and the current 20 milliamps, the input would be (200 x .02) equal 4 watts. In_ practice, there is no necessity for these meters in a low-powered transmitter, however. The plate dissipation of the valve is the input it will radiate in the form of heat without overheating, while the efficiency of the valve is the amount of radio-frequency output given as a percentage of the input. Candidates may be. asked for simple definitions such as these. Another likely question is one on modulation, such as "Explain with a diagram the Heising method of modulation." In a Morse valve transmitter using pure direct current power supply, the continuous wave sent out is unmodulated, and is sintply started and stopped by means of the Morse key. For telephony, however, this wave, now known as the carrier wave, is on the air continuously, and is modulated by voice or music. Thus, its amplitude, or the energy it contains, is varied in accordance with changes in sound waves in the form of variations in ‘the current input or output of the transmitter. The latter variations are repro duced in the receiver. and converted back into sound waves. ‘The commone est method of modulating is the Heising, or constant current, method. With this, besides the valve that generates the carrier wave, there is ane other one of equal size, the modulator valve, and the plates of these two are fed through an iron-core choke from a common power supply, as shown in Fig. I. This choke keeps the total plate current and the voltage across both valves invariable. A microphone is connected through 2 transformer between the grid and fila ment of the modulator valve, and when spoken into varies the grid voltage of this valve at speech frequency, thus causing changes in the plate current. As the sum of the plate currents drawn by both valves is invariable, the current of the oscillator must become smaller as that of the modulator becomes greater, or greater as the modulator current becomes smaller, with corresponding variations in the input. ‘ Thus as the speech varies the grid voltage and plate current of the modulator, the input to the oscillator is inversely varied, which correspondingly affects its output. .Also, as explained, the carrier wave will thus be modulated by the speech. Heising and similar

forms are known as plate modulation systems, but there is also ‘the grid system, which is, however, not widely used. In this, variations in the bias on the grid of the oscillator tube are caused by speech through a microphone, thus correspondingly fluctuating the plate current and causing modulation. . The percentage of modulation of a transmitter is the percentage that the modulation strength is of the carrier strength, as heard in a receiver. In other words it is the variation in the amplitude of the wave, caused by modulation, as compared with the amplitude of the carrier wave. It follows that a carrier wave may also be modulated by using an alternating or pulsating direct current power supply to the oscillator valve, since the input is rapidly changed with the alternating voltage, with similar fluctuations in the output. This modulation evolves in a hargh, chopped-up signal, which is hard to read on Morse, and the voltage variation of the input ereates much interference by causing the frequency of the wave to vary, and side-band frequencies to be set up. That is why pure direct current power supply is necessary for an oscillator to give a smooth, musical signal of a single frequency, and questions upon this subject are often set in the examination, e.g. "What are the disadvantages of using A.C. power supply to a transmitter?" or "What is the best type of current for supply to a transmitter, and why?" Measurement of Frequency. T is advisable to know something about the frequency measurement, @ common question being: "How would you measure the frequency of a transmitter by means of an absorption wavemeter?’ The two chief types of wavemeters for this purpose are the heterodyne and the absorption types, the former being explained in the "Listeners’ Guide." The absorption’ wavemeter, shown "in Fig. II, consists ~- of a coil tuned by a calibrated variable condenser, with a torch ‘bulb in the circuit. When the meter is placed near the transmitter, the coii absorbs the greatest amount of rf. energy when the two circuits are in resonance, or tuned to the same. wavelength. ‘This energy absorbed causes the bulb to light up, so that if the condenser is adjusted until the bulb lights up .most, the, wavemeter and, ‘transmitter are tuned to the same ,wavelength, which. is shown on the. calibrated condenser scale. A .frequent question is: "Describe two -meters‘for the measurement of radio-frequency current." Such meters measure by the heating effect of the r.f. current, and the types are the hotwire meter, described in the "Guide," and‘ the thermo-couple meter. The

latter (Wig. IIT) makes use of the principle that when two: dissimilar metals are heated an H.M.F. is produced between them. ‘The current to be. measured is run through a small resistance AB, which heats a junction, C, of two such dissimilar metals, D and BD, and the resultant H.M.F.: is taken to an ordinary. moving-coil meter which shows a reading dependant on the heat produced by the R.F. current. Besides such questions as already mentioned, there are usually two or three on the elementary electrical principles, which are in the "Guide," or

have appeared in the "Record." They may be on Ohm’s Law, -calculation of resistances and capacities, in series and parallel, voltage drop through resistances, magnetic fields of bar magnets, inductance, and the fundamental theory of valves. They are all quite simple, highly technical answers not being required. Amateur Radio Regulations. . The only remaining part of the exam. is that on the Amateur Radio Regulations. Though this is important, it is the easiest part, for it is simply a matter of learning the few laws given below, which constitute the chief regulations.

Firstly, there are the wavebands on which amateurs are allowed to transmit. They are as follow:Kilocycles. Metres. 1715 to 2000 150 to 175 3500 to 4000 75 to 85.7 7000 to 7800 41.1 to 42.9 14000 to 14400 20.83 to 21.48 28000 to 30000 10 to 10.71 Special permission is required to operate on the bands below 80, metres, the latter being the only band in which telephony is allowed, in New Zealand. An amateur must execute the usual declaration of secrecy, and must not commit to writing any public correspondence he may hear. If he should hear a distress signal (SOS) and has reason to believe it has noi been intercepted by a ship or shore station, he must take steps to advise the nearest Government station, or, failing this, a responsible P. and T. officer. Amateurs must be able to recognise the interference warning signal sent by a Government station, AAAAQRM (here following a number indicating minutes) and must close down for the number of minutes indicated. The use of waves other than continuous waves, such as damped waves (spark transmission), is prohibited for amateurs, .and all transmitters must be inductively coupled to the antenna. Power supply to the transmitter must not be alternating current, and the transmitter should be adjusted and tuned at such times as to cause a minimum of interference. A log record, showing the .hours during which the station is in operation, and a note of any special signal received, must be kept, while the station must not be used in any way to send or receive messages calculated to cause a loss of revenue to the P. and T. Department. The operator shall not transmit anything of a seditious, profane, obscene, libellous or offensive nature, or any communication of a false or misleading character, in particular a false SOS signal. All stations shall be open to inspection by a radio inspector, and the station license must be displayed in a prominent position. Examples of questions on these regulations are: "What are the amateur bands in metres and kilocycles, and what are their conditions of use?’ or "What are the classes of matter an amateur is not allowed to transmit?" ; or "If you heard an SOS signal and had reason to believe it had not been intercepted, what steps would you take?" Finally, the fee for sitting the examination is five shillings, and an application form may be obtained through a post office. Should any further information pertaining to the examination be required. it will be supplied on application addressed to -the writer at the "Record" office. In the next article there will be a description and discussion of a low-powered transmitter suitable for the beginner, Hw te