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D

DAC : Also known as D/A and D-to-A. Digital to Analogue converter. A device that converts digital signals into analouge signals.

dB : Decibel - the ratio of two power measurements.

dBd : dB relative to a dipole. Also known as dBD

dBi : dB relative to a theoretical isotropic (point) source.

dBm: The power compared to a 1 milliwatt (1mW) source, expressed in decibels (dB)

dBo : Optical gain. An unofficial term used by some amateurs working with transmission of data using light.

dBuv : a measure of voltage compared to one microvolt. 0dBuv = one microvolt.

De or DE : "this is" or "from" - for example an operator may use VL2TK de VK4ZW .......

DF : Direction finding. Also known as ARDF and "fox hunting", the use of triangulation and directional antennas to find a hidden transmitter. May be done recreationally, or as a means of locating the source of problematic radio frequency interference.

Diplexer : A frequency splitting device used to couple two transceivers to either a single antenna or a dual band antenna.

Dipole : An antenna with two collinear elements, usually of equal length, with feedpoint in the centre. Commonly used as the driven elements for more complex antennas such as the yagi or log-periodic, a dipole on its own is omnidirectional if mounted for vertical polarisation but has a figure-8 directional pattern if mounted horizontally.

Dish : A highly directional antenna, parabolic in shape. Often used at microwave frequencies.

Domino EX : a digital mode that uses a variant of MFSK known as IFK for transmission of information.

Downlink : The channel or frequency used for satellite to earth communications.

DPSK : Differential Phase Shift Keying - a form of BPSK

DRM : Digital Radio Mondiale. A system of digital broadcasting developed by a consortium of manufacturers, researchers, broadcasters and governments.

DSP : Digital Signal Processing. The digital processing of signals in filtering, noise reduction etc.

DTMF Dual Tone Multi Frequency - the allocation of a unique tone pair to each button on an appliance (made up of two frequencies - high and low) that allows a computer to recognize the tone. Originally used on a wide scale in landline telephony to allow tone dialling using a small keypad on a telephone or handset, but has been used in amateur radio to remotely control repeaters, autopatch, IRLP or Echolink nodes.

Dual Band Antenna : An antenna designed to be used on two amateur Bands.

Dummy Load : An artificial antenna that does not radiate. A non-inductive power resistor, a dummy load is connected in place of the transmitting antenna and used when aligning transceivers.

Duplex : Transmit and receive are on two different frequencies - often use in repeaters with a shift (difference) of 600Hz.

Duplexer : A device that allows an antenna to transmit and receive simultaneously.

DVM : Digital voltmeter.

DXCC : DX Century Club

DX : Distance or distant station. Originally "distant exchange", from landline telephony. On HF radio, normally used to refer to a station on another continent or in an exotic location.

DXpedition : An expedition by amateurs to a location that may be geographically or physically remote and from where amateur contacts are rare.

Dynamic Range : How well a receiver can handle very strong signals wthout overloading.