TERMS AND EXPRESSIONS

Manawatu Times, Volume LII, Issue 3615, 16 September 1927, Page 11

TERMS AND EXPRESSIONS

SIMPLE EXPLANATIONS.

The following list is taken from Harmsworth’s ‘Wireless Encyclopedia:—

Damping Moment. —Term used for one of tli e intrinsic contents of a vibration galvanometer.

Daylight Effect. —Expression used to describe the difference of normal range of reception during- the daylight 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 phenomenon.

D.C.O.—This is the standard abbreviation for the Insulated wire known as double cotton covered wire. Dead Beat.—When 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 th e 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 successively 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 down at it reaches its final defloctlonai point, beyond which it passes but a little way, if at all. In the second case the needle would come to rest very much more quickly than In the first, and would be termed dead beat.

Dead Crystal.—Name used to describe a crystal without sensitive spots. Dead Earth.—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 unwanted parts, of the winding of an inductance coll. Deck Insulator.—Typo of insulator used on board a ship for insulating the aerial at the point where it is led through the deck or roof of the radio cabin.

Detector Valve.—A thermionic valve used for rectifying radio frequency oscillatibns. 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 arc 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. —ln electricity the ’word generally denoted a non-conductor of electricity—i.e., an insulator. It is usually confined .to non-conductors when their function is to separate neighbouring conductors at different potentials.

Direct Coupling.—The coupling between two or more inductances or circuits when the connection is made by metallic contact. Direction Finder.—Apparatus so constructed as to indicate from which direction signals arc 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 coupled coils arc common to both circuits.

Direct Tight Coupling.—Term ’used in cases in which the turns of wire in two metallically connected inductances are in an appreciable ratio to one another.

Double Cotton Covered Wire. —Abbevlated 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 having two distinct inductances, one usually designed for ohort wave-lengths and the other for ongcr wave-lengths. Double Throw Switch. —A me■hanical device whereby a current of ■lectricity. reaching the switch by one terminal, can bo bandied on from one or other of two separate contact -mints from which Ihe current is 'aken to any desired point on the pparatus. Down Lead. —Name given to the vim leading from the aerial to the adio instrument.