Glossary of Terms and acronyms

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. The term is generally used in the USA where specific frequencies set aside for TV are used; in Europe spectrum originally intended for telecommunications use is used to deliver analogue DBS services and the term DTH is generally used instead.

dBi:
The dB power relative to an isotropic source.

dBW:
The ratio of the power to one Watt expressed in decibels. For non-technical people, the term most commonly occurs in describing the signal strength on the ground of a transmission from a satellite. Typically, the signal strength needed for DTH or DBS transmissions is 52 dBW or more.

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.

Decoder:
A television set-top device that 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 that is used in conjunction with digital transmissions.

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 that extracts or "demodulates" the "wanted" signals from the received carrier.

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

Digital Terrestrial Television:
European term for terrestrial television that makes use of COFDM transmission techniques to provide multi-channel TV through a standard TV aerial.

DirecPC:
Form of Internet access service which uses the telephone line to connect a user with an Internet Service Provider and a satellite link to download requested information back to the consumer. Seen as an interim form of Internet access before development of Ka-band type satellite switched services.

DVB:
Digital Video Broadcasting - European term to describe European digital broadcasting standards for cable, satellite and terrestrial TV defined through the Digital Video broadcasting group. The latter is an association of broadcasters, transmission companies and consumer and professional electronics manufacturers.