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F/D

Ratio of antenna focal length to antenna diameter.  The higher the ratio the shallower the dish.

FDMA (Frequency Division Multiple Access)

Refers to the use of multiple carriers within the same transponder where each uplink has been assigned a specific frequency slot and bandwidth.  This is usually employed in conjunction Frequency Modulation.

Feed

This term has several key meanings when used in the context of satellite and terrestrial communications.
First and foremost is it's use to describe the actual signal being transmitted by the station or satellite to receivers.
It is also used to describe the assembly that delivers the signal to a satellite dish or terrestrial link for transmission.  This transmit assembly may contain a subreflector and a feedhorn in the case of Cassegrain systems or a stand-alone feedhorn in Prime Focus and Offsat systems.

Feedhorn

The component of an antenna, particularly in satellite dishes, that transmits and/or receives the signal  reflected or collected from the main surface of the dish.   In receive configurations the reflected signal is then processed by LNA's or LNB's before being passed on to the receiver.

Field

Half of a video frame, 262.5 horizontal lines (NTSC).

Fingerprinting

The process of visibly or invisibly displaying the IRT/IRD unit address on the active portion of the video signal. This technique is used to identify the source of the material if recorded and later replayed or distributed.

Fixed or Fail Key

An encryption designation indicating that the service is encrypted with a key known to all decoders of a given make and model.. Any decoders of a particular type can receive the programming.

FM (Frequency Modulation)

A modulation method whereby the baseband signal varies the frequency of the main carrier wave.

FM Threshold

The point at which the input signal power is sufficient to enable the receiver demodulator circuitry to successfully detect and recover a good quality television picture from the incoming video signal.  Using threshold extension circuitry a typical satellite receiver will successfully deliver good pictures with an incoming carrier/noise ratio of 7 dB.  Below this threshold analog signals experience a type of random noise called "sparkles" which begin to appear in the video picture.  In digital transmissions a drop below the FM Threshold usually results in a total loss of the signal.  

The FM Threshold also applies to terrestrial radio signals and is manifested by noise or signal drop on your radio receiver.  Some radios have a local/distant, particularly in automobile stereos, have a selector that allows you to choose threshold extension for use in improving the reception of distant stations.

Focal Length

The distance from a feedhorn transmit assembly or a subreflector to the center of the dish.

Focal Point

The area toward which the primary reflector directs and concentrates the signal.   Ideally the receive focal point is at the receive horn assembly.   Transmissions from satellite dishes have a transmit focal point that coincides with the position of the satellite.

Footprint

The area on the earth's surface where reception characteristics for a particular satellite and transponder are optimal.  This is based on the EIRP of the signal from a given satellite and transponder and different transponders on the same satellite will often have different footprints of signal strength.  Reception deteriorates gradually from the center of the footprint.  Depending on variable factors such as positioning and type of feed assembly satellite footprints may be roughly circular or elliptical in shape.  In elliptical configurations some transponders are aimed off-center in order to provide a wider coverage area.  Footprints may change over the course of time as the satellite ages and orbital orientation drifts.

Forward Error Correction (FEC)

Circuitry that adds unique codes to digital signals at the source of the transmission which enable receivers to detect and correct errors.

Frame

One complete video picture. In NTSC, takes place in one-thirtieth of a second and is made up of 525 lines and two fields.

Frame Rate

The rate at which frames are to be output from the decoding process

Frequency

The number of times that an alternating current goes through it's complete cycle in one second of time.  One cycle per second is referred to as one hertz; 1000 cycles per second = one kilohertz; 1,000,000 cycles per second = one megahertz; and 1,000,000,000 cycles per second = one gigahertz.

Frequency Coordination

A process used to eliminate possible frequency interference between different satellite and terrestrial microwave transmit systems.  In North America this activity relies upon a computerized service that utilizes and extensive database to analyze potential microwave interference problems between fixed installations using the same frequencies and transportable earth-stations using C-Band frequencies. This problem stems from the fact that the C-Band frequency range is used by telephone companies, cable companies and satellite transmission facilities.  New C-band installations of any type and all transportable C-Band satellite uplinks must obtain frequency coordination information for given locations before being allowed to begin transmissions in order to determine if potential interference problems exist.

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