# UK Amateur Radio ## Foundation Licence 2002
### Technical terms & abbreviations
For information only, for the assessment, candidates will not be required to know any terms or concepts which are not in the syllabus itself AC Alternating Current. Current which changes direction, at a rate known as the "frequency". Also used as an adjective, as in AC voltage, AC circuit etc. Aerial Same as 'antenna'. Widely used in the UK in relation to domestic radio and TV etc. ('Antenna' is used for most engineering purposes.) AF Audio Frequency. AMU Antenna Matching Unit. Same as ATU. AM Amplitude Modulation. A method of modulation where the amplitude of the carrier is varied. Antenna A radiator or collector of electromagnetic energy. Attenuator A device for reducing the level of RF or AF signals. ATU Antenna (or Aerial) Tuning Unit. Device to tune an antenna to resonance, and match it to the transmitter. Balun Balance-to-unbalance transformer. Often used to connect an unbalanced (coaxial) feeder to a balanced antenna, e.g. a dipole. BCI Interference to broadcast radio reception. Breakthrough Used (particularly by radio amateurs) to describe interference caused by the legitimate radiation from a transmitter entering a piece of equipment which has insufficient immunity. Bond To connect together by a low resistance path. Braid The woven outer conductor of coaxial cables. The woven screen around screened cables. A woven (flat) conductor which gives a large conductor area. Capacitor A component which stores energy as an electric field, and consists of two metal plates that are a small distance apart but insulated from each other. Opposite charges are stored on each plate. See Tuned Circuit. Characteristic impedance This is a property of transmission lines. For a coaxial line it depends on the diameters of the inner and outer conductors and the dielectric in between. Typical values for coaxial line are 50 ohm for general radio use and 75 ohm for TV downlead. Choke An inductor (coil) used to restrict the flow of AC current. Code Often used by amateurs (particularly in the USA) as an abbreviation for Morse code. CW (Morse) Continuous Wave Morse sent by keying the carrier on and off. It is considerably more effective than voice when operating under difficult conditions, and for low power operation. dB Abbreviation for decibel. A convenient way of expressing powers, voltages etc. as a logarithmic ratio. DC Direct Current. Current which always flows in the same direction. Also used as an adjective as in DC voltage, DC circuit etc. Dummy Load A resistor used in the place of an antenna to enable a transmitter to be tested or adjusted without radiating a signal. Earth (radio) A conductor buried in the ground. Assumed to be at zero potential for radio frequencies. Earth (mains) The protective conductor (at nominal earth potential). EMC Electromagnetic Compatibility. The ability of electronic devices and systems to operate without mutual interference. EMI Electromagnetic Interference. ERP Effective Radiated Power. The power radiated in the direction of maximum radiation. The power supplied to the antenna multiplied by the gain of the antenna. Feeder A transmission line used to transfer the power from a transmitter or ATU to the antenna. Usually a coaxial cable or open-wire line. Ferrite Magnetic material which is used to increase the inductance of an inductor/coil. It can be made with a wide range of properties to suit different frequencies and applications. Usually it has a high electrical resistance. A "Ferrite Rod" is often used as part of the antenna in medium and long wave receivers. Ferrite Ring Choke A choke made by winding a lead on to a ring-shaped ferrite core. Ferrite Ring Braid-Breaker A ferrite ring choke made by winding co-axial cable on to a ferrite ring. Used in TV down leads and similar applications. It can be viewed as impeding unwanted signals picked-up on the braid of the co-ax while leaving the wanted signals (inside the coax) unaffected. Filter A circuit which allows some frequencies to pass with a small loss, while attenuating other frequencies. They are often made up from several tuned circuits. FM Frequency Modulation. A form of modulation in which the frequency is varied. Ground Same as earth. Harmonic (In radio) Unwanted signals which are at an integer multiple of the transmitter carrier frequency. HF High Frequency. The range of frequencies between 3.0MHz and 30MHz Immunity (In EMC) The ability of a piece equipment to operate satisfactorily in the presence of a strong RF field. Inductor A component which stores energy as a magnetic field when a current is flowing through it, and consists of a coil of wire. It is used in AC circuits, see Tuned Circuit. Intermods Short for 'intermodulation products'. Outputs (usually unwanted) caused by two or more signals mixing. Instability Unwanted oscillation, or a tendency to oscillate. Mains The domestic electricity supply. Modem A Modulator/Demodulator. A circuit which takes data and modulates it onto a carrier signal or demodulates it and recovers the data. See TNC. Pass band The band of frequencies passed by a filter with small loss. PCB Printed circuit board. PCB Polychlorinated biphenyl. (Oil used at one time in certain types of transformers and capacitors etc. Highly toxic; can be absorbed through the skin.) PME Protective Multiple Earthing. An earthing arrangement used in some parts of the UK electricity distribution system. Polarisation (of radio wave) The direction of the electric field. Usually linear (e.g. horizontal or vertical). There are also complicated situations where the polarisation rotates. PSK Phase Shift Keying. A form of data modulation which the phase of the carrier is varied. Similar to frequency shift keying. PSK31 A form of data transmission developed for amateur communications using a home computer in conjunction with an amateur transceiver. Like CW (Morse) it is very effective in difficult conditions and for low power operation. PTT Push (or Press) To Talk. The circuit which switches the transmitter from receive to transmit and vice versa. Q Codes International abbreviations originally defined for the maritime service to facilitate communications in Morse code. All are three letters starting with Q. Amateurs have adapted some Q codes for informal use. e.g. QSY (change frequency), QRT (stop transmitting), QRU (I have run out of things to talk about) etc. Resonance A situation where energy is stored at one frequency in a tuned circuit. See Tuned Circuit. RF Radio Frequency RFI Radio Frequency Interference. Screen Conductive enclosure or partition. Sometimes used instead of 'braid' to describe a woven outer conductor of a coaxial cable. Secondary Status (When a band is shared more than one service) So far as amateurs are concerned, it is the service which does not have 'right of way'. On a shared band, where the Amateur Service is a secondary user, amateurs must take care not to cause interference to the primary user. Selectivity The ability to reject unwanted signals while receiving the wanted one. See Tuned Circuit. Shield Same as screen. Splatter Spurious emissions relatively close to the nominal carrier frequency. Can be caused by overdriving an SSB transmitter. Spurious Emission Unwanted radiation that is outside the normal bandwidth of the transmission. It can include harmonics and other signals or noise. SSB Single SideBand. A power and spectrum efficient form of amplitude modulation in which only the minimum necessary part of the signal is transmitted. It is widely used for speech communications. Stop Band The range of frequencies which are attenuated by a filter. (Frequencies outside the pass band.) SWR Standing Wave Ratio. An indication of the forward and reflected power in transmission lines, particularly antenna feeders. TNC Terminal Node Controller. A type of modem used in Packet radio which modulates the data onto audio tones which can be connected to the audio input of a transmitter and decodes the audio tones from a receiver and converts them back into data. Transmatch Same as ATU. Transmission Line Conductors arranged to convey RF energy between different parts of an installation. Coaxial cable is the most commonly used type of transmission line. Tuned Circuit A combination of an inductor and a capacitor which stores energy at one particular frequency - the Resonant frequency. It can be used to select a signal on one frequency and reject signals on other frequencies. Its behaviour is analogous to a bell or a tuning fork. Tuning (a receiver) Adjusting the receiver to select the wanted signal. TVI Interference to TV reception. UHF Ultra High Frequency. The range of frequency between 300MHz and 3000MHz VCR Video Cassette Recorder. VHF Very High Frequency. The range of radio frequencies between 30MHz and 300MHz.

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