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DAMA

Demand-Assigned Multiple Access - A highly efficient means of instantaneously assigning telephony channels in a transponder according to immediate traffic demands.

dBi

The dB (decibel) power in relation to an isotropic source

DBS

Direct Broadcast Satellite - Refers to the satellites and services that provides multiple channel television service to homes nationwide using small home dishes.   DBS uses a digital transmission and encryption format.

dBW

The ratio of the power one Watt expressed in decibels.

Decibel (dB)

The standard unit used to express the ratio of two power levels.  In communications it is used to represent either the gain or loss of power between the input and output devices.

Declination

The offset angle of an antenna from the axis of it's polar mount as measured in the meridian plane between the equatorial plane and the antenna main beam.

Decoder

A device which enables encrypted signals to be converted to viewable signals.   This may refer to both analog and digital encryption systems.

Decoder Unit

This term refers to the new generation of television set-top units that accept digital and analog television signals.

Decoding

There are many types of decoding protocols which vary from system to system.  It is the process by which a particular decoder converts an encoded analog signal or digital bit-stream back into it's usable video or audio components.

Deemphasis

Reinstatement of a uniform baseband frequency response following demodulation.

Delay

The time it takes a signal to go from the sending station through the satellite to the receiving station.  The approximate delay time of a signal through a geosynchronous satellite is close to one-quarter of a second.  This is due to the fact that the signal travels at the speed of light.  The signal makes a round trip of approximately 44, 500 miles and also has an additional slight delay while being processed through the satellite.

Demodulator

A receiver circuit which extracts or "demodulates" the desired signal information from the received carrier.

Deviation

The modulation level of an FM signal as determined by the amount of frequency shift (measured in MHz) from the center frequency of the main carrier.

Digital

Information converted into bits of data for transmission through any medium such as wire, fiber optic cable, satellite or over the air techniques.

Digital Component Video

Digital video that uses separate color components such as, Y,Cr,Cb or RGB.

Digital Composite Video

Digital video that is a digitized waveform of composite NTSC or PAL video signals with specific values assigned to the sync, blank and white levels.

Digital Compression

Digital compression involves the use of algorithms to reduce the bandwidth necessary to store or transmit a digital video signal or other digital information.

Digital Speech Interpolation (DSI)

A method of tranmitting telephony 2.5 to 3 times more efficiently through the use of a digital format.  This process takes advantage of the fact that during a conversation the actual voice content makes up only 40 % of the conversation with pauses between words and sentences make up the other 60 %.  In essence it is a form of time compression to represent the pause periods.

Dolby

Dolby A, B, C and Dolby SR are electronic processing that are used to increase the signal-to-noise ratio and reduce unwanted frequencies.  This process specifically targets the frequency range of the tape hiss that is inherent in the recording of analog signals.

Downlink

Any satellite dish capable of receiving digital or analog broadcasts from satellites in orbit.

Dual Spin

A spacecraft design which allows the satellite to spin in place in order to provide altitude stabilization while allowing the antenna to remain motionless through the use of a motor and bearing system.  This allows the rotation of the satellite while keeping the antenna array oriented correctly in relation to the earth.  This system allows the creation of a "spin-stabilized satellite".

Dynamic

A term used to describe any signal that is undergoing changes in amplitude or frequency. 

Dynamic Range

Dynamic range is defined by the amount of change between the upper and lower extremes of the amplitude or frequency alterations of an audio signal.

 

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