D/A
Digital to Analog

DAC
Digital to Analog Converter. A device that converts a digital input signal to an analog output signal carrying equivalent information

Data
Digitally represented information, which includes voice, text, facsimile and video

dB
Decibel. The standard unit used to express the relative strength of two signals. When referring to a single signal measured at two places in a transmission system, it expresses either a gain or loss in power between the input and output devices

dBmV
Decibel Millivolt. The level at any point in a sytem expressed in dBs above or below 1 millivolt/75 ohm standard is said to be the level in decibel-millivolts or dBmV. Zero dBmV is equal to 1 millivolt across an impedance of 75 ohms

DC
Direct Current (see Current, Direct)

DCE
Data Communications Equipment. In common usge, synonymous with modem; the equipment that provides the functions required to establish, maintain and terminate a connection as well as the signal conversion required for communications between the DTE and the telephone line or data circuit

DCL
Data Carrier Level

DC Resistance
See Resistance

Demand
(1) The measure of the maximum load of a utility's customer over a short period of time
(2) The load integrated over a specified time interval

Derating Factor
A factor used to reduce the current carrying capacity of a wire when used in environments other than that for which the value was established

Detector
A fiber optic device that picks up light from the fiber and converts the information into an electical signal

Dielectric
An insulating (nonconducting) medium

Dielectric Breakdown
Any change in the properties of a dielectric that causes it to become conductive. Normally the failure of an insulation because of excessive voltage

Dielectric Constant
The property of an insulation which determines the electrostatic energy stored per unit volume for unit potential gradient. It is expressed as a ratio. "K" for air is 1.0, while that for polyethylene is 2.3. Therefore, the capacitance of polyethylene is 2.3 times that of air. It is also referred to as Specific Inductive Capacity or Permitivity

Dielectric Dispersion
The change in relative capacitance due to a change in frequency

Dielectric Heating
The heating of an insulating material when placed in a radio-frequency field, caused by internal losses during the rapid polarization of molecules in the material

Dielectric Loss
The power dissipated in a dielectric as the result of the friction produced by molecular motion when an alternating electric field is applied

Dielectric Strength
The maximum voltage which an insulation can withstand without breaking down; usually expressed as a gradient in V/mil (volts per mil). Polyethylene for example has a dielectric strength of about 800 V/mil

Dielectric Strength Testing
A common test performed on electrical products which is often called hi-pot testing. A voltage higher than normal operating voltage is applied across the insulation. This test can increase product reliability by detecting faulty workmanship

Digital
Refers to communications procedures, techniques and equipment by which information is encoded as either a binary "1" or "0"; the representation of information in discrete binary form, discontinuous in time, as opposed to the analog representation of information in variable, but continuous, waveforms

DIN
Deutsches Institut für Normung. The German Standard for many products

Dip Coating
An insulating coating applied to the conductor by passing the conductor through an applicator containing liquid insulating medium

Direct Burial Cable
A cable installed directly in the earth

Direct Capacitance
The capacitance measured directly from conductor to conductor through a single insulating layer

Directional Coupler
A passive device used in a cable system to divide or combine unidirectional RF power sources

Direction of Lay
The lateral direction, designated as left-hand or right-hand, in which the wires of a conductor as they receed from an observer looking along the axis of a conductor

Dispersion
The variation of the refractive index of an optical fiber with wavelength, causing light of different wavelengths to travel at different velocities in the fiber

Dissipation Factor
Energy lost when voltage is applied across an insulation. The cotangent of the phase angle between voltage and current in a reactive component. Dissipation factor is quite sensitive to contamination and deterioration of insulation. Als known as Power Factor

Distortion Factor
An undesired change in waveform as the signal passes through a device

Distribution Cable
(1) In a CATV system, the transmission cable from the distribution amplifier to the drop cable
(2) In an electric power system, provides low voltage service to the customer

Disturbed Conductor
A conductor that receives energy generated by the field of another conductor or an external source such as a transformer

Disturbing Conductor
A conductor carrying energy whose field(s) create spurious energy in another conductor

Download
The process of loading software into the nodes of a network from one node or device over the network media

Drain Wire
An uninsulated wire in contact with a shield throughout its length, used for terminating the shield

Drawing
In wire manufacture, pulling the metal through a die or series of dies to reduce diameter to a specified size

Drop Cable
In a CATV system, the transmission cable from the distribution cable to a dwelling

DSR
Data Set Ready. One of the control signals on a standard RS-232-C connector. It indicates whether the data communications equipment is connected and ready to start handshaking control signals so that transmission can start

DTR
Data Terminal Ready. An RS-232 modem interface control signal (sent from the DTE to the modem on pin 20) which indicates that the DTE is ready for transmission and which requests that the modem be connected to the telephone

Dual Cable
A two-cable system in broadband LANs in which coaxial cables provide two physical paths for transmission, one for transmit and one for receive, instead of dividing the capacity of a single cable

Duct
An undergound or overhead tube for carrying electrical conductors

Duofoil ®
Belden trademark for a shield in which metallic foil is applied to both sides of a supporting plastic film

Duplex
Two way data transmission on a four-wire transmission cable

Duplex Cable
A cable composed of two insulated single conductor cables twisted together