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# A

In a given set of radio channels, the RF channel whose characteristic frequency is situated next above or next below that of a given channel.

Note 1 – The adjacent channel situated above the given channel is known as the “upper adjacent channel” and the one below it as the “lower adjacent channel”.

Note 2 – Two adjacent channels may have part of the frequency spectrum in common and this may be referred to as frequency overlap.

In a given set of radio channels, the RF channel whose characteristic frequency is situated next above that of the upper adjacent channel or next below that of the lower adjacent channel.

### Alternated (polarization)

In a given set of radio channels, this term refers to an arrangement of channels in which two adjacent channels have orthogonal polarizations.

### Antenna directivity diagram

A curve representing, in polar or Cartesian coordinates, a quantity proportional to the gain of antenna in the various directions in a particular plane or cone.

### Antenna gain

The ratio, usually expressed in decibels, of the power required at the input of a loss free reference antenna to the power supplied to the input of a given antenna to produce, in a given direction, the same field strength of the same power flux-density at the same distance. When not specified otherwise, the gain refers to the direction of maximum radiation. The gain may be considered for a specified polarization. Depending on the choice of the reference antenna, a distinction is made between:

(a) absolute or isotropic gain (Gi ), when the reference antenna is an isotropic antenna isolated in space;

(b) gain relative to a half-wave dipole (Gd ), when the reference antenna is a half-wave dipole isolated in space whose equatorial plane contains the given direction;

(c) gain relative to a short vertical antenna (Gv ), when the reference antenna is a linear conductor, much shorter than one quarter of the wavelength, normal to the surface of a perfectly conducting plane which contains the given direction.

### Assigned frequency

The centre of the assigned frequency band.

### Assigned frequency band

The frequency band within which the emission of a station is authorized; the width of the band equals the necessary bandwidth plus twice the absolute value of the frequency tolerance. Where space stations are concerned, the assigned frequency band includes twice the maximum Doppler shift that may occur in relation to any point of the Earth’s surface.

Note1 – For certain services, the term “Assigned channel” is equivalent.

# B

### Band (occupied)

The frequency band such that, below the lower and above the upper frequency limits, the mean powers emitted are each equal to a specified percentage β/2 of the total mean power of a given emission. Unless otherwise specified by the ITU-R, for the appropriate class of emission, the value of β/2 should be taken as 0.5%.

### Bandwidth (necessary)

For a given class of emission, the width of the frequency band which is just sufficient to ensure the transmission of information at the rate and with the quality required under specified conditions.

### Bandwidth (occupied)

The width of a frequency band such that, below the lower and above the upper frequency limits, the mean powers emitted are each equal to a specified percentage β /2 of the total mean power of a given emission.
Unless otherwise specified by the ITU-R for the appropriate class of emission, the value of β/2 should be taken as 0.5%.

(Symbols: Lb or Ai)

The transmission loss that would occur if the antennas were replaced by isotropic antennas with the same polarization as the real antennas, the propagation path being retained, but the effects of obstacles close to the antennas being disregarded.

Note 1 – The basic transmission loss is equal to the ratio of the equivalent isotropically radiated power of the transmitter system and the power, available from an isotropic receiving antenna.

Note 2 – The effect of the local ground close to the antenna is included in computing the antenna gain, but not in the basic transmission loss.

# C

### Carrier power (of a radio transmitter)

The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle taken under the condition of no modulation.

Note – With some types of modulating signals the concept of carrier power is meaningless.

### Channel spacing

In a given set of radio channels, the difference in frequency between the characteristic frequencies of two adjacent channels.

### Channel, RF channel (radio frequency)

Part of the radio spectrum intended to be used for an emission and which may be defined by two specified limits, or by its centre frequency and the associated bandwidth, or by any equivalent indication.

Note 1 – Usually the specified part of the radio spectrum is that which corresponds to the assigned frequency band.

Note 2 – A radio frequency channel may be time-shared in order to allow radiocommunication in both directions by simplex operation.

Note 3 – In some countries and certain texts of the existing RR, the term “channel” is also used to denote a radio frequency circuit or, in other words, two associated radio frequency channels within the meaning of the proposed definition, each of which is used for one of the two directions of transmission.

### Class of emission

The set of characteristics of an emission, designated by standard symbols, e.g. type of modulation of the main carrier, modulating signal, type of information to be transmitted, and also if appropriate, any additional signal characteristics.

### Client/server model

Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfills the request.

### Co-channel

Refers to the use of the same RF channel by two or more emissions.

### Cross-polarization

The appearance, in the course of propagation, of a polarization component which is orthogonal to the expected polarization.

### Cross-polarization discrimination

For a radio wave transmitted with a given polarization, the ratio at the reception point of the power received with the expected polarization to the power received with the orthogonal polarization.

Note – The cross-polarization discrimination depends both on the characteristics of the antennas and on the propagation medium.

### Cross-polarization isolation

For two radio waves transmitted at the same frequency with the same power and orthogonal polarization, the ratio of the co-polarized power in a given receiver to the cross-polarized power in that receiver.

# D

### Depolarization

A phenomenon by virtue of which all or part of the power of a radio wave transmitted with a defined polarization may no longer have a defined polarization after propagation.

### Diversity reception

A reception method in which one resultant signal is obtained from several received radio signals which convey the same information but for which the radio path or the transmission channel differs by at least one characteristic such as frequency, polarization, or the position or orientation of antennas.

Note 1 – The quality of the resultant signal can be higher than that of the individual signals, due to the partial decorrelation of propagation conditions over the different radio paths or transmission channels.

Note 2 – The term “time diversity” is sometimes used to refer to the repetition of a signal or part of a signal over a single radio path or transmission channel

### Diversity reception (frequency)

Diversity reception in which several radio channels are used with appropriate frequency separations.

Note – If the channels are situated in different frequency bands, the frequency diversity is said to be “cross-band diversity”.

### Diversity reception (space)

Diversity reception in which several antennas are used at appropriate distances from each other in a radio station.

Note – For line-of-sight radio-relay systems, separation is generally vertical, whereas for trans-horizon radio-relay systems, it is generally horizontal.

### Double sideband . . . (DSB)

Pertaining to a transmission or emissions where both the lower and upper sidebands resulting from amplitude modulation are preserved.

# E

### Effective monopole radiated power (e.m.r.p.) (in a

The product of the power supplied to the antenna and its gain relative to a short vertical antenna in a given direction.

Note – The reference antenna, when fed with a power of 1 kW, is considered to radiate an e.m.r.p. of 1 kW in any direction in the perfectly conducting plane and produces a field strength of 300 mV/m at 1 km distance (equivalent to a c.m.f. of 300 V).

### Effective radiated power (e.r.p.) (in a given dire

The product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction.

Note - The reference antenna, when fed with a power of 1 kW, is considered to radiate an e.r.p. of 1 kW in any direction in the equatorial plane and produces a field strength of 222 mV/m at 1 km distance.

### Emission

Note - For example, the energy from the local oscillator of a radio receiver if transferred to external space, is a radiation and not an emission.

### Emission (harmonic)

Spurious emissions at frequencies which are whole multiples of those contained in the and occupied by an emission.

### Emission (out-of-band)

Emission on a frequency or frequencies immediately outside the necessary bandwidth which results from the modulation process, but excluding spurious emissions.

### Emission (spurious)

Emission on a frequency or frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information.

Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products, but exclude out-of-band emissions.

### Emissions (unwanted)

Emissions consisting of spurious emissions and out-of-band emissions.

### Equivalent isotropically radiated power (e.i.r.p.)

The product of the power supplied to the antenna and the antenna gain in a given direction relative to an isotropic antenna (absolute or isotropic gain).

Note - The isotropic antenna, when fed with a power of 1 kW, is considered to provide an e.i.r.p. of 1 kW in all directions and to produce a field strength of 173 mV/m at 1 km distance.

# F

### Frequency (assigned)

The centre of the assigned frequency band.

### Frequency (reference)

A frequency having a fixed and specified position in respect to the assigned frequency.

### Frequency tolerance

The maximum permissible departure by the centre frequency of the frequency band occupied by an emission from the assigned frequency or, by the characteristic frequency of an emission from the reference frequency.

Note - The frequency tolerance is expressed in parts in 10 6 or in hertz.

### Full carrier

Pertaining to a transmission or emission with amplitude modulation where, by convention, the power of the sinusoidal carrier component is no more than 6 dB below the peak envelope power.

Note 1 - Double-sideband amplitude-modulated emissions normally comprise a full carrier with a power level exactly 6 dB below the peak envelope power at 100% modulation.

Note 2 - In single-sideband full-carrier emissions, a carrier at a power level of 6 dB below the peak envelope power is emitted, to enable the use of a receiver designed for double-sideband full-carrier operation.

# G

### Gain (antenna)

The ratio, usually expressed in decibels, of the power required at the input of a loss free reference antenna to the power supplied to the input of a given antenna to produce, in a given direction, the same field strength of the same power flux-density at the same distance. When not specified otherwise, the gain refers to the direction of maximum radiation. The gain may be considered for a specified polarization.

Depending on the choice of the reference antenna, a distinction is made between:

(a) absolute or isotropic gain (Gi ), when the reference antenna is an isotropic antenna isolated in space;

(b) gain relative to a half-wave dipole (Gd ), when the reference antenna is a half-wave dipole isolated in space whose equatorial plane contains the given direction;

(c) gain relative to a short vertical antenna (Gv ), when the reference antenna is a linear conductor, much shorter than one quarter of the wavelength, normal to the surface of a perfectly conducting plane which contains the given direction.

### Ground wave

A radio wave basically determined by the properties of the ground which propagates in the troposphere and which is mainly due to diffraction around the Earth.

# I

### Interfering source

An emission, radiation, or induction which is determined to be a cause of interference in a radio communication system.

### Interleaved

In a given set of radio channels, this term refers to the insertion of additional channels between the main channels (or each RF channel and its adjacent channels), the characteristic frequencies of the additional channels being different from those of the main channels by a specified value, generally a significant portion (e.g. one half) of the nominal channel spacing.

# L

### Line-of-sight propagation (LOS)

Propagation between two points for which the direct ray is sufficiently clear of obstacles for diffraction to be of negligible effect.

# M

### Mean power (of a radio transmitter)

The average power supplied to the antenna transmission line by a transmitter during an interval of time sufficiently long compared with the lowest frequency encountered in the modulation taken under normal operating conditions.

### Multipath propagation

Propagation between a transmission point and a reception point over a number of separate propagation paths simultaneously.

# N

### Noise (in telecommunication)

Any variable physical phenomenon apparently not conveying information and which may be superimposed on, or combined with, a wanted signal.

Note - The term "radio-frequency noise" is defined in this Recommendation.

# O

### Offset

In a given set of radio channels, this term refers to a change of the characteristic frequency of a radio-frequency channel in relation to its nominal frequency, by a specified value which is generally small compared to the channel spacing.

# P

### Point-to-point communication

Communication provided by a link, for example, a radio-relay link between two stations located at specified fixed points.

### Protection margin

The difference between the signal-to-interference ratio and the protection ratio, these ratios being expressed in logarithmic form.

Note 1 - Generally, care is taken to ensure that the difference between the ratios is positive to ensure reliability of communication.

### Protection ratio

The minimum value of the signal-to-interference ratio required to obtain a specified reception quality under specified conditions and at a specified point.

Note 1 - Various ITU-R Recommendations contain definitions for specific applications. The minimum value is usually laid down in these Recommendations and in other international agreements.

# R

Pertaining to the use of radio waves.

A time-varying electromagnetic phenomenon having components in the radio- frequency range, apparently not conveying information and which may be superimposed on, or combined with, a wanted signal.

Note 1 - In certain cases a radio-frequency noise may convey information on some characteristics of its source, for example its nature and location.

Note 2 - An aggregate of signals may appear as radio-frequency noise, when they are not separately identifiable.

The locus of points at which the direct rays from a point source of radio waves are tangential to the surface of the Earth.

Note - As a general rule, the radio and geometric horizons are different because of atmospheric refraction.

A telecommunication facility of specified characteristics between two points provided by means of radio waves.

Any electromagnetic phenomenon having components in the radio-frequency range, which may degrade the performance of a device, equipment or system, or affect adversely living or inert matter.

Note - A radio-frequency disturbance may be a radio-frequency noise, an unwanted signal or a change in the propagation medium itself.

Degradation of the reception of a wanted signal caused by a radio-frequency disturbance.

Note 1 - Often man-made noise is not included in interference.

Note 2 - The English words "interference" and "disturbance" are often used indiscriminately; the expression "radio-frequency interference" is also commonly applied to a radio-frequency disturbance or to an unwanted signal.

Radiocommunication system between specified fixed points operating at frequencies above about 30 MHz which uses tropospheric propagation and which normally includes one or more intermediate stations.

Telecommunication by means of radio waves.

### Ray path

At each point, the path tangential to the direction of propagation of energy at this point.

Note 1 - The concept of ray is the basis of the geometrical optics which, when applicable, permits the substitution of simple relationships for Maxwell's equations.

Note 2 - In some cases, several paths may exist between two points.

Note 3 - In an isotropic medium, the ray path is a trajectory orthogonal to the wavefronts and the term "ray" is often defined as this trajectory. In an anisotropic medium, the trajectories orthogonal to the wave fronts do not always coincide with physical paths between a source and a receiving point and should not be called rays.

### Reference frequency

A frequency having a fixed and specified position in respect to the assigned frequency.

# S

### SAF Tehnika

Company, makes stuff...

### Sending (in telecommunication), transmission (depr

The production of a signal at an input port of a transmission line or into a transmission medium.

### Severely errored second (SES)

Time interval of 1 s during which a given digital signal is received with an error ratio greater than a specified value.

### Sideband

A frequency band lying above or below a sinusoidal carrier frequency and containing spectral components of significance produced by modulation.

### Signal

A physical phenomenon one or more of whose characteristics may vary to represent information.

Note - The physical phenomenon may be for instance an electromagnetic wave or acoustic wave and the characteristic may be an electric field, a voltage or a sound pressure.

### Simplex, half duplex (deprecated); simplex

Designating or pertaining to a method of operation in which information can be transmitted in either direction, but not simultaneously, between two points.

### Single sideband . . . (SSB)

Pertaining to a transmission or emission where only either the lower sideband or the upper sideband resulting from amplitude modulation is preserved.

### Space division

A technique whereby a separate individual transmission path is used for each transmission channel for example in multiplexing, switching or multiple access operations.

### Switching (in telecommunication)

The process of temporarily associating functional units, transmission channels or telecommunication circuits for the purpose of providing a desired telecommunication facility.

# T

### Terrestrial station

(Symbols: Ll or Al ) The ratio, usually expressed in decibels, between the radio-frequency power supplied by the transmitter of a radio link and the radio-frequency power supplied to the corresponding receiver in real installation, propagation and operational conditions.

### Trans-horizon propagation

Tropospheric propagation between points close to the ground, the reception point being beyond the radio horizon of the transmission point.

Note - Trans-horizon propagation may be due to a variety of tropospheric mechanisms such as diffraction, scattering, reflection from tropospheric layers. However ducting is not included because in a duct there is no radio horizon.

### Tropospheric propagation

Propagation within the troposphere and by extension, propagation beneath the ionosphere, when not influenced by the ionosphere.

A quasi-horizontal stratification in the troposphere within which radio energy of a sufficiently high frequency is substantially confined and propagates with much lower attenuation, than would be obtained in a homogeneous atmosphere.

### Tropospheric-scatter propagation

Tropospheric propagation by scattering from many inhomogeneities and/or discontinuities in the refractive index of the atmosphere.

# W

### WEB server

A Web server is a program that, using the client/server model and the World Wide Web's Hypertext Transfer Protocol (HTTP), serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests). Every computer on the Internet that contains a Web site must have a Web server program.

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