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F

F/D : The ratio of focal length to diameter of a parabolic dish antenna.

Feedline : The wire or cable that joins a transmitter or receiver to an antenna. Also known as a transmission line.

FET : Field-effect transistor, a semiconductor in which current between source and drain is controlled by voltage applied to a high-impedance gate

Field day : An annual event in which portable stations are deployed, contacts made and new or prospective operators encouraged to get on the air.

Filter : An electric circuit (often called a network) that allows certain frequencies to pass but rejects (attenuates) other unwanted frequencies.

FM (Frequency Modulated or Frequency Modulation): The shape of the carrier signal is changed (modulated) by the frequency of another signal, usually the voice of the operator.

Frequency: The number of complete waves that pass a reference point per second. Expressed in Hertz (Hz)

Frequency Shift Keying: A digital mode in which the signal is broken into "chunks". Each chunk is then shifted in frequency slightly above or below the central carrier. Effectively, frequency modulation used to carry a digital signal.

Fuse : A device that self destructs when too much current passes through it - used for circuit protection.