FILTER.--Inductance coils or condensers or both which (1) prevent troublesome voltages from acting on the different circuits, and (2) smooth out alternating currents after they have been rectified.
FILTER REACTOR.--See Reactor, Filter.
FIRE UNDERWRITERS.--See Code, National Electric.
FIXED GAP.--See Gap.
FLEMING VALVE.--A two-electrode vacuum tube.
FORCED OSCILLATIONS.--See Oscillations, Forced.
FREE OSCILLATIONS.--See Oscillations, Free.
FREQUENCY, AUDIO.--(1) An alternating current whose frequency is low enough to operate a telephone receiver and, hence, which can be heard by the ear. (2) Audio frequencies are usually around 500 or 1,000 cycles per second, but may be as low as 200 and as high as 10,000 cycles per second.
- Carrier.--A radio frequency wave modulated by an audio frequency wave which results in setting of three radio frequency waves. The principal radio frequency is called the carrier frequency, since it carries or transmits the audio frequency wave.
- Commercial.--(1) Alternating current that is used for commercial purposes, namely, light, heat and power. (2) Commercial frequencies now in general use are from 25 to 50 cycles per second.
- Natural.--The pendulum and vibrating spring have a natural frequency which depends on the size, material of which it is made, and the friction which it has to overcome. Likewise an oscillation circuit has a natural frequency which depends upon its inductance, capacitance and resistance.
- Radio.--(1) An oscillating current whose frequency is too high to affect a telephone receiver and, hence, cannot be heard by the ear. (2) Radio frequencies are usually between 20,000 and 2,000,000 cycles per second but may be as low as 10,000 and as high as 300,000,000 cycles per second.
- Spark.--The number of sparks per second produced by the discharge of a condenser.
GAP, FIXED.--One with fixed electrodes.