Glossary of Wireless Terms

Radio Record, Volume II, Issue 5, 17 August 1928, Page 31

Glossary of Wireless Terms

/ From week to week we give here asection of the glossary of wireless t ternis from the "Listener’s Guide." y

aa. a F H.T.B.-Short for high tension battery. See "B Battery." HAND-CAPACITY.-An effect which interferes with the tuning of a receiving set, created by the proximity of the hand to a variable tunjng condenser. To prevent this trouble, firstly, see that the moving plates of the tuning condenser are connected to earth. Keep the condenser as far away from the hand as possible, if necessary using an ebonite rod for a tuning spindle. If these precautions do not eliminate the trouble it may be necessary to shield the back of the panel with copper sheet, taking particular cave that no part of the set comes in contact with it except the earth terminal to which it should be connected. HARMONICS.-In radio, harmonics refer to the incidental waves mostly noticeable in undampéed ("spark") wave operation, although sometimes very pronounced in broadcast receeption. These harmonies differ in length and frequency from the true and original operative wave of such transmitters. At» times, listeners will hear the harmonics of high power long wave stations, while their tuners are set for much shorter waves. The harmonics of the 600 metre wave--length in general use for ship Morse communieation are as follow :-~- nn

it will De observed that the first yaria‘tion from the original wavelength is Galled the "second harmonic," and so on. Ao ascertain, say, the eighth harmonic of a station operating on, for instance, 400 metres, divide 400 by 8, and the result, 50, gives the wavelength of the harmonic. HEATER TUBE OR VALVE.-A valve specially designed for sets driven direct from A.C. mains, has a heater which is electrically separate from the filament, but heats the latter mechanic-

ally and causes it to perform its usual functions. This is a high pitched note when the heats are rectified to render them audible. It is this action which is the explanation of "howling" between an oscillating receiver and a broadcast transmitter, or between two oscillating receivers. When receiving signals from a broadcast transmtter by the heterodyne method, the beats are produced at an inaudible frequency, and the detector valve used rectifies the "beats,’? and renders the music, etc., audible. Such a receiver is known as "superheterodyne." Thus, if the wave from the incoming station has a frequeney of 80,000 per second, and the locally produced oscillations are produced at 31,000 per second, the "beat" or "heteordyne" note will be 1000 per second. HENRY.-The unit of self-inductance, being that inductance which will so retard any change in the value of a current that it takes 1 second for 1 volt to raise the current in a circuit by 1 ampere. In tuning circuits the Henry is too hig, and measurements are usually reckoned in terms of milli- or micro-henries. HETERODYNE.-A system for the reception of continuous wave signals. The receiving circuit is artificially supplied with oscillations at a frequency slightly different from that of the inceming waves. The two series of oscillations alternately add and subtract as they came into or go out of step with one another. This produces pulsations of amplitude at an audible frequency, known as "beats." A similar effect can sometimes be observed if two adjjacent notes on a piano are struck simultaneously. HERTZIAN WAVES. — Electro-mag-netic waves (the basis of radio transmission and reception), named after their discoverer, Prof. Heinrich Hertz. BIGH FREQUENCY (H.F.) OR RADIO FREQUENCY.-A term applied to alternations or waves avhich océur at frequencies too high for audibility ; sometimes called "Radio Frequency." High frequency may be taken to inelude al! frequencies above 10,000 per second.

Second harmonic . 309 metres Third " 20 " Fourth " 150 -,, Fifth " 120 39 Sixth » 100 Seventh 85.7 ,, Highth " 75 "? Ninth " 66.6 ,, Tenth " 60 , .- Hte., ete.