Glossary of Wireless Terms

Radio Record, Volume II, Issue 11, 28 September 1928, Page 29

Glossary of Wireless Terms

rom week to week we give here asection of the glossary of wireless terms from the "Listener's Guide."

PICK-UP, ELECTRO-MAGNETIC.-A device for attaching to a gramophone to enable the output from the record to be passed through the audio stages of a radio receiving set, and thereby amplified before issuing from the radio loudspeaker. The unit is, in itself, merely a reed type loudspeaker or phone unit with an attachment to the reed to’ enable gramophone needles to be held into position. When the needle is vibrated against the surface of the record, the reed in turn is moved correspondingly as the action in turn alters, producing a flux in the iron of the magnets over which the windings are wound. The flux introduces an _ alternating H.M.F. in the windings surrounding the magnets, which is of frequency corresponding to the vibrations activating the needie. The pick-up generates minute voltages which require to be stepped up before they are of sufficient magnitude to actuate the diaphragm or cone of a loudspeaker. To increase the voltages generated in the pick-up, the ordinary audio amplifier is brought into operation, either as a separate unit or plugged into the broadcast receiver, so that two audio stages iad

or, in some cases three, are brought into operation. Mechanical means are used in the ordinary gramophone to amplify the sound vibrations produced in the sound box, and of course absolute fidelity of reproduction cannot exist in such Circumstances. Power valves will handle this volume without overloading, and the output will be much purer in consequence. Then the loudspeaker must be brought into consideration if perfect reproduction is to be expected. It should be capable of good reproduction of both the high-pitched and low-pitched sounds. POLES.-The opposite ends of a magnet or terminals of a battery are spoken of as poles; in the former as north and south poles, and in the latter as positive and negatives; termed also plus and minus polarity, respectively. POTENTIOMETER.-A compact device for varying the potential applied to different parts of wireless circuits. POWER AMPLIFICATION.-A system of low-frequency amplification which makes use of valves and transformers specially designed to deal with considerable energy; is essential to efficient loudspeaker operation. ee