I Signal

One of the two color video signals which modulate the color subcarrier. It represents those colors ranging from reddish orange or cyan.

IDR

International Digital Route. The digital equivalent of the analog FDM/FM voice service used by INTELSAT.

IDRS(S)

Tracking and Data-Relay Satellite (System) used by NASA.

IF (or i.f.)

Intermediate Frequency. A middle range frequency generated after down conversion in any electronic circuitry including a satellite receiver. The majority of all signal amplification, processing and filtering in a receiver occur in the IF range.

IFL

Inter-Facility Link. Anything from a cross-site transmission line to a complete data network.

IMD

lnterrnodulation Distortion (in nonlinear system).

Impedance

The total opposition that a circuit offers to the flow of alternating current or any other varying current at a particular frequency. It is a combination of resistance R and reactance X, measured in ohms.

Impulse Pay-Par-View

Impulse pay-per-view (IPPV) is a feature of a decoder that allows an authorized subscriber to purchase a non-time scrambled program at will. IPPV shows are selected by a button on the decoder or its remote control unit.

Inclination

Angle between orbital plane of satellite and equatorial plane of the Earth.

Inclinometer

An instrument used to measure the angle of elevation to a satellite from the surface of the earth.

Inductance

The property of a circuit or circuit element that opposes a change in current flow, thus causing current changes to Jag behind voltage changes. It is measured in henrys.

Injection Locking

Low-cost technique for phase-locking a cavity or resonator oscillator to a crystal source, to improve its frequency stability.

INSAT

Indian National Satellite System.

Insertion Loss

The amount of signal energy lost when a device is inserted into a communication line. Also known as "feed through" loss.

Insulation

A material having high resistance to the flow of electric current. Often called a dielectric in radio frequency cable.

Insulation Resistance

The ratio of the applied voltage to the total current between two electrodes in contact with a specific insulation, usually expressed in megohms - M feet.

INTELSAT

The International Telecommunication Satellite Consortium, a body of 154 countries working towards a common gold of improved worldwide satellite communications.

Interference

An undesired signal intercepted by a TVRO that causes video and/or audio distortion.

Interferometer Feed

Antenna feed generating controlled pattern of sidelobes and nulls, to permit use of small antennas with closely satellites.

Interlaced Scanning

A scanning technique to minimize picture flicker while conserving channel bandwidth. Even and odd numbered lines are scanned in separate fields both of which when combined paint one frame or complete picture.

Intersatellite Link

A transmission path directly between two communications satellites.

IPA

Intermediate Power Amplifier (Uplink Transmitter).

ISDN

Integrated Services Digital Network. A high quality global telecommunications network based on digital technology. ISDN is designed to allow subscribers to access a multiplicity of communications services through a single point or connector in the network.

Isolation

The measure of separation (as dB or power ratio) between two potentially interfering signals, e.g. in difference beams or on different polarizations.

Isolation Loss

The amount of signal energy lost between two ports of a device. An example is the loss between the feed through port and the tap/drop of a top-off device.

Isolator

Transmission-line component which passes signals with low loss in a preferred direction, while presenting high attenuation in the reverse direction.

Isotropic

reference for antenna gain measurements.

ITS

Insertion Test Signal (also VITS) for monitoring a channel's video performance parameters.

IUS

Internal Upper Stage (for GEO launches) A type of PKM. are scanned in separate fields both of which when combined paint one frame or complete picture.