TERMS AND EXPRESSIONS

Shannon News, 4 October 1927, Page 4

TERMS AND EXPRESSIONS

SIMPLE EXPLANATIONS. The following list is taken from Harmsw'orth’s ‘Wireless Encyclopedia:— Damping Moment. —Term used for one *of th e intrinsic contents of a vibration galvanometer. Daylight Effect. —Expression used to describe the difference of normal range of reception during the day : light hours as compared with the night. It is well known that radio signals are received over greater distances at night than in the daytime, and there have been many theories advanced to account for this phono-, menon. D.C.C.—This is the standard abbreviation for the Insulated wire known as double cotton covered wire. Dead Beat. —Whi n the needle of a galvanometer or similar measuring instrument deflects from its zero position it may behave in two different ways. It may take a smart swing from the impulse received, and overshoot the mark owing to the presence of inertia in the moving parts in which case it first swings beyond its final resting place, retreats to a point somewhat short, and success ively oscillates to and fro in swings of diminishing amplitude until it at last comes to rest. Or it may move away from the zero point, on receiving its impulse, in a more sluggish manner, the rapidity of its action slowing dow r n at it reaches its final cioflectional point, beyond which ii masses but a little way, if at all. In the s conrl case the needle w'ould oome to rest very much more quickly than in the first, and w'ould be termed dead beat.

Dead Crystal.—Name used to describe a crystal without sensitive spots.

Dead Earthy —This term is used in a number of ways, but more commonly in the case of a complete short circuit. Dead End Effect. —The result on an oscillatory circuit of the presence of idle turns of an inductance.

Dead End Switch.—Name given to a switch used for cutting out un wanted parts of the winding of an inductance coil.

Deck Insulator. —Type of insulator used on board a ship for insulating (he aerial at the point where it is led :hrough the deck or roof of the radio cabin.

Detector Valve.—A thermionic valve used for rectifying radio fre(juoncy oscillations. It consists of a grid, a plate, and a filament, the whole enclosed within a glass bulb. D.F. —This is the usual abbreviation for direction finder. Dial—ln radio work dials are used to control the movement of the condensers, and various other portions movable in the set.

Diaphragm.—A thin disc, usually of soft iron, found in telephones and microphones, for the production or detection of electrical pulsations. Dielectric. —In electricity the word generally denoted a non-conductor of electricity—i.e., an insulator. Il is usually confined to non-conductors when their functioh is to separate neighbouring conductors at different potentials.

Direct Coupling-.—The coupling beIween two or more inductances- or circuits when the connection is mad • by metallic contact. Direction Finder. —Apparatus so constructed as to indicate from which direction signals are coming. Direct Loose Coupling.—Term Applied to a metallic coupling- between two circuits, when either th e distance between the two circuits or when only a few turns in each of the coupl'd coils are common to both circuits.

Dlrte: Tight Coupling.—Term used

• s j n which the turns of wire ;, i !\vo metallically connected induc*rmcos are in an appreciable ratio to one another.

Double Cotton Covered Wire. —Aboeviatod at D.C.C. this expression refers to a particular type of wire with a double coating of cotton insulating. Double Pole Switch.—A mechanical switch for interrupting both poles of the source of supply of electrical currents simultaneously by the movement of one handle or switch arm.

Double Range Receiver.—A variable inductance haying two distinct inductances, one usually designed for short wave-lengthg and the other for longer wave-lengths. Double Throw Switch. —A mechanical device whereby a current of electricity, reaching the switch by one terminal,.*can be handled on from one. or other of two separate contact points from which th c current is taken to any desired point on the apparatus. Down Lead. —Name given to the wire lending from the aerial to the radio instrument.