RADIO TERMS

Sun (Auckland), Volume II, Issue 421, 1 August 1928, Page 6

RADIO TERMS

Inductance (abbreviated, I.). —Inductance, like capacity, plays a very prominent part in radio circuits. It is the property of a coil of wire which tends to prevent any change in the value of current flowing through "it. It governs tlio frequency, and therefore the wave length, of a circuit. The unit of inductance is the henry. In radio work the millihenry and the microhenry are the more practical terms used. Induction.—The transference of energy from one circuit to another by means of electro-magnetic phenomena. Insulator.—A non-conductive material, and one through which an electric current will not pass. lon.—A gaseous atom having a surplus or deficiency of electrons. Kilowatt (abbreviated, k.w.). —One thousand watts, a unit of power. Loop Aerial.—A small frame aerial used for indoor reception, thus eliminating both outdoor aerials and earth connections. It gives very marked directional effects. Megohm.—One. million ohms. Microfarad (Abbreviated Mfd.).—One millionth part of a farad, and the practical unit of capacity. Microphone.—A sound magnifier, or an instrument used in both wire and radio telephony to vary the current in circuit by means of speech. Milliampere (Abbreviated M.A.).— The thousandth part of one ampere. Neutralising Condenser. —A condenser of small capacity used in radio frequency circuits to neutralise the internal capacity existing between the plate and grid elements of the valve. Neutral-formers. —Specially wound radio frequency transformers with a tapped secondary for external connection to the neutralising condenser. Ohm. —The unit of electrical resistance. Ohm's Law.—The fundamental law of electrioity. It is that the current in amperes flowing through a circuit is equal to the pressure in volts divided by the resistance in ohms. Oscillations.—Alternating currents of very high frequencies are called electrical oscillations. If the amplitude of a series of oscillations is constant, they are called continuous or undamped waves, but if the amplitude is not constant, as in the spark method, they are called damped waves. Potential.—Referring to electrical pressure. See E.M.P. and Volt. Radiation.—The transmission of energy through space in the form of electro-magnetic waves. Radio Frequencies.—Frequencies corresponding to vibrations not normally audible to the human ear. All frequencies above 10,000 cycles per second are termed radio frequencies. See Audio Frequencies. Reactance.—Opposition offered to the flow of a varying current by a condenser (capacity reactance), or an inductance (inductive reactance). Rectifier.—An apparatus which converts alternating current (A.C.) into pulses of direct current (D.C.); Tungar, and Kenotron apparatus are employed for rectifying purposes. Certain metallic crystals also have rectifying action when used as detectors in radio reception. Regenerative Circuit. —A radio circuit comprising a valve so connected that after detection, the signal introduced in the plate circuit is led back to or caused to react upon the grid circuit, thereby increasing the original energy of the signal received by the grid and greatly amplifying the response to weak signals. In reception, the leading back of plate energy to the grid for further strengthening is usually accomplished by means of a coil placed close to the secondary of the receiving tuner. The small coil is called the reaction coil. Resistance.—Opposition to the flow of an electric current through a conducting medium. All metals have more or less electrical resistance. Copper is used universally for both electrical and radio work on account of minimum re-

sistance, comparative low cost and ready availability'. The unit of resistance is the ohm. I Resonance.—A very important func- [ tion of radio circuits. The theory of electrical resonance s similar to that of acoustics, readily demonstrated by the tuning forks, when one tuning fork will not respond to another unless it is of the same key or pitch. Rheostat.—A variable resistance employed to control or regulate current flow. Selectivity.—ln radio work, the power of being able to select any particular wave length to the exclusion of others. Sharp Tuning.—Where a very slight change of a tuner or tuning system will produce a marked effect in the strength of signals. Transformer.—A device used in electrical and radio work for the transference of energy. Thus wc have Power Transformers, Amplifying Transformers, Telephone Transformers, Oscillation Transformers. Tuning.—The act of altdHng capacity or inductive values in a radio circuit so as to bring the circuit into resonance. In radio receiving, the greatest signal strength is obtained when the product of the inductance and capacity value of the receiver matches that of the transmitter. Undamped.—A train of high frequency oscillations of constant amplitude as continuous waves of C.W. Valve. —In radio work, applies to a glass tube exhausted of air and containing essentially a filament, a plate positively charged, to which electrons are attracted, and a grid, inserted between the filament and the plate, for controlling the amount of electronic flow. This action of the valve plays three leading functions in radio work, i.e., detection, amplification and generation of high frequency electro-magnetic waves. Velocity of Waves.—Wireless waves travel through space at the speed o! 156,000 miles a second, or 300,000 kilometres a second. Volt {Abbreviated V).—'The unit of electric pressure. Voltmeter. —An instrument for measuring the voltage across an electric current. Wave-meter. —An instrument for measuring the wave length of a transmitting station. Watt (Abbreviated W).—The unit or electric power. To find power in watts mutiply voltage by amperage; 746 watts equal to one horse-power; 1,000 watts equal one kilowatt (K.W.). Wave Length.—Radio waves in their passage through the ether travel in undulating wave form, similar to water waves. When the wind is blowing hard and steady the distance between each wave crest is comparatively long while if the wind is blowing monmildly and in short spurts, the distance between wave crests is shorter and we have short waves. In radio substitn ~ the wind for the transmitter and yo have a similar action.

BROADCASTING ON LIGHT MAINS

Efforts are being made in Europe to apply the principle of the carrier wave telephone, such as that recently installed so successfully between Melbourne and Sydney, to the trans®*** sion of musical programmes. Ther* are so many different broadcasting stations working in Europe that more wave length channels are avail" able for new services, and some other means of providing these services most be found. The solution of the problem which is being investigated the transmission of programmes over trie light mains. One of the fit* commercial uses of the carrier wav* telephone system was the sion of speech over high-transmta**®* lines of electric light and power com panies. The use of the transmij*** lines in this way saved the cost __ extra telephone line. Communi ratio over the lines can. of course, oe tained while they are also fra.n s thousands of horse power of ei energy. There are indication electric light services in will be used before long for di ing programmes. A simple plus serted in a socket, and conne a cord to a special receiver, wotna able the programmes to be P* from the lines, and no mte with the lighting service y<\ ul ? b ;7\h* Alternatively, it is suggested - over programmes could be distrib the telephone lines. Tins a tejfbe done without interrupting tD b is phone service, and one cou "l« \rithtelephone for an ordinary - out interrupting the program®” ing received from it.