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

DBS
Direct broadcast satellite. Refers to service that uses satellites to broadcast multiple channels of television programming directly to home mounted small-dish antennas.

dBi
The dB power relative to an isotropic source.

dBW
The ratio of the power to one Watt expressed in decibels.

De-BPSK
Differential Binary Phase Shift Keying

De-QPSK
Differential Quadrature Phase Shift Keying.
Decibel (dB)
The standard unit used to express the ratio of two power levels. It is used in communications to express either a gain or loss in power between the input and output devices.

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

Decoder
A television set-top device which enables the home subscriber to convert an electronically scrambled television picture into a viewable signal. This should not be confused with a digital coder/decoder known as a CODEC which is used in conjunction with digital transmissions.

Deemphasis
Reinstatement of a uniform baseband frequency response following demodulation.

Delay
The time it takes for a signal to go from the sending station through the satellite to the receiving station. This transmission delay for a single hop satellite connection is very close on one-quarter of a second.

Demodulator
A satellite receiver circuit which extracts or "demodulates" the "wanted "signals from the received carrier.

Deviation
The modulation level of an FM signal determined by the amount of frequency shift from the frequency of the main carrier.

Digital
Conversion of information into bits of data for transmission through wire, fiber optic cable, satellite, or over air techniques. Method allows simultaneous transmission of voice, data or video.

Digital Speech Interpolation
DSI - A means of transmitting telephony. Two and One half to three times more efficiently based on the principle that people are talking only about 40% of the time.

Discriminator
A type of FM demodulator used in satellite receivers.

Dithering
he process of shifting the 6-MHz satellite-tv signal up and down the 36-MHz satellite transponder spectrum at a rate of 30 times per second (30 Hertz). The satellite signal is "dithered" to spread the transmission energy out over a band of frequencies far wider than a terrestrial common carrier microwave circuit operates within, thereby minimizing the potential interference that any one single terrestrial microwave transmitter could possibly cause to the satellite transmission.

Down-Converter
That portion of the Fixed Satellite Service (FSS) television receiver that converts the signals from the 4-GHz microwave range to (typically) the more readily used baseband or intermediate frequency (IF) 70-MHz range.

Downlink
The satellite to earth half of a 2 way telecommunications satellite link. Often used to describe the recieve dish end of the link.

DSU
Data service unit. A device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as T1 or E1. The DSU is also responsible for such functions as signal timing. DSU is freqnetly coupled with a CSU (see above) as CSU/DSU.

DTV
Digital Television

Dual Spin
Spacecraft design whereby the main body of the satellite is spun to provide altitude stabilization, and the antenna assembly is despun by means of a motor and bearing system in order to continually direct the antenna earthward. This dual-spin configuration thus serves to create a spin stabilized satellite.

Duplex Transmission
Capability for simultaneous data transmission between a sending station and a receiving station.

DVB
Digital Video Broadcasting - The European-backed project to harmonise adoption of digital video.

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