Glossary of Wireless Terms

Radio Record, Volume I, Issue 52, 13 July 1928, Page 3

Glossary of Wireless Terms

TNDER this heading we will give regulariy sections of the glossary of wireless terms which is a prominent feature of the N.Z, Radio Listzuers’ Guide. In that book, although set in the smallest type, it occupies some 18 pages, and is definitely in our opinion the most comprehensve and complete glossary on modern lines which has been made available in the Dominion. For. the benefit of our readers the glossary will be reprinted in our columns,

COUNTERPOISE.-A system of Wires (usually insulated and placed direcily under an aerial), which is employed as a substitute for an "earth," A counterpoise is frequently used in conjunction with transmitting aerials in ordc: te reduce the effective resistance, aud in receiving broadcasting to afford greater selectivity and to reduce powerline and other electrical interference. COUPLER, LOOSE-A convenient form of tuning instrument in which two cous ere used, energy being transferred from one to the other electro-magnetical-ly; ig very close together they are "tightcoupled"; if far apart, "loose-coupled." Usuaily the primary is fixed in position and the secondary, being of smaller dia«meter, slides in or out of the primary, thus varying the degree of coupling. The tuning of the primary and secondary may be accomplished by taps, sliding econturts, or external condensers, or by the fact that the secondary sliding inside the primary not only alters the coupling but also the self capacity and therefore the tuning. COUPLING. Represenis the means by which energy is transferred from one cirenit to another. A "direct"? coupling | refers to a condenser or inductance coil, being common to both cireuits, thereby linking them together, An "indirect"? coupling refers to no actual connection between the two other than by magnetic induction due to the proximity of two coils, one being included in each cireult. A "tight" or "loose" coupling refers purely to the quality of coupling in & given set of circumstances, Thus, an indirect coupling may be made very tighi, while a direct coupling can be quiie loose. he amount of linkage between the two circuits is known as the "mutual inductance," where the cireuits are indirectly linked. CRYSTAL DETECTOR.--A detector which depends for its action upon the fact that the contact between a crystal and «& metal, or between two crystals, wil only carry an appreciable current in on» direction, Thus trains of highfreqneney oscillations can be converted into trains of unidirectional impulses, which produce an audible sound in a receiver telephone. The "crystal set" ix the most inexpensive form of radio re-. ceiving equipment, but it has generally only wn-exceedingly limited range for bropfeast reception and, as a rule, will

receiye only local broadeasting, unless yalve amplifiers are employed in conjunction with the crystal. Crystals eapable of performing the necessary function of rectification ave of many forms. While there are some quite as efiicient as yalves in this respect, the valve has the advantage that it simultaneously amPlifies the feeble signals. CURRENT.-An electric current is a movement of negative electrons, driven by an electro-motive force. A current cannot flow unless there is an electromotive force to drive it, and a conducting path for it to flow along. ‘The unig of electric current is the ampere. Current is a distinetive effect representing quautity at a given moment. To obtain a measure of power, the current ov quantity for a given time must be considered as well as the voltage or pressure. Pressure multiplied by quantity gives power in "watts." A direct curvent (D.C.3 is one which flows continuously in a given direction. See "Alternating, Oseillating, and Impulsive Currenis. CYCLE,--See "Alternating Current"; also "Kilocyele."’ DAMPING.--When resistance is introduced by any means into a circuit for the purpose of simplifying tuning or to render the cireuit less liable to burst into oscillation, the circuit is said to be "damped." Damping tends to flatten tuning and to reduce signal strength, thus reducing the general efficiency, and should be resorted to only as a last desperate remedy for undesirable superselectivity or wuncontrollability. See "Aneriodic." DC. (DIRECL CURRENT).--See Current," D.C, WIRK (DOTBLE COTTOXCOVERED Wi2E)-A very ‘sual abbreviation referring to the type of insulation covering a particular gauge of copper wire, DEAD-END,-Conusideruble loss is occasioned by the use of a large coil for low wavelengths, the greater proportion of the coil being unused, Tnless this unused portion or "dead-end" is shortcircuited, if tends fo absorb much of the signal strength.