Engineer Radio Electronic Communication key terms

The attenuation of a radio signal as it spreads spherically between isotropic antennas in unobstructed space, growing with the square of distance and the square of frequency.

An ellipsoidal volume around the straight line between transmitter and receiver where most signal energy travels; obstruction of the first zone causes diffraction loss beyond simple path loss.

Additional attenuation caused when a signal bends around an obstacle such as a building edge or hill crest, filling the shadow region behind it with reduced field strength.

Fluctuation of received signal level caused by interference among several propagation paths of differing length and phase, producing constructive and destructive combining at the antenna.

A statistical model for received envelope in multipath channels with no dominant line-of-sight path, where signal amplitude follows a Rayleigh distribution and deep fades occur frequently.

A fading model used when a strong direct path coexists with scattered paths, giving a dominant deterministic component plus random scatter, typical of line-of-sight links.

The time difference between the earliest and latest significant multipath arrivals; it sets the maximum symbol rate before intersymbol interference becomes severe without equalisation.

The range of frequencies over which the channel response is approximately flat and correlated; signals wider than it experience frequency-selective fading.

The ratio of power radiated in a specified direction to that radiated by a lossless isotropic reference antenna fed the same power, usually expressed in dBi.

The angular width of an antenna's main radiation lobe measured between the two directions where radiated power falls to half its peak value, i.e. minus 3 dB.

The product of transmitter power delivered to the antenna and antenna gain relative to isotropic, expressed in dBW or dBm; the key figure for regulatory emission limits.

A measure of impedance mismatch on a feed line, equal to the ratio of maximum to minimum voltage along it; 1:1 means perfect match, higher values indicate reflected power.

The ratio in decibels of incident power to reflected power at a port or junction; a large positive value indicates a good impedance match.

A matrix description of a multi-port network in terms of incident and reflected travelling waves, used to characterise amplifiers, filters and antennas at radio frequencies.

The reduction in signal power, in decibels, caused by inserting a component such as a filter or cable into a transmission path, measured with matched source and load.

The degradation in signal-to-noise ratio caused by a receiver or amplifier, expressed in decibels as the ratio of input to output signal-to-noise ratio.

The combined noise figure of several stages in series, dominated by the first stage's noise figure and gain according to the Friis formula.

A theoretical input or output level at which the fundamental and third-order intermodulation products of an amplifier would be equal; a measure of linearity.

The input or output power level at which an amplifier's actual gain falls one decibel below its small-signal linear gain, indicating onset of saturation.

Generation of spurious signals at sums and differences of two or more input frequencies when a nonlinear device is driven, potentially causing in-band interference.

A receiver architecture that mixes the incoming signal with a local oscillator to a fixed intermediate frequency, where filtering and amplification are easier and more selective.

A frequency that mixes with the local oscillator to produce the same intermediate frequency as the wanted signal, allowing unwanted signals to pass unless rejected by front-end filters.

A feedback loop that adjusts receiver gain to keep output level roughly constant despite large variations in received signal strength, preventing overload and clipping.

The range of input signal levels over which a receiver or component performs acceptably, from the noise floor up to the level where distortion or saturation becomes excessive.

The total noise power present in a receiver or measurement system, set by thermal noise, bandwidth and noise figure, below which signals cannot be reliably detected.

A receiver's ability to reject a strong signal in the neighbouring channel while receiving the wanted signal, largely determined by intermediate-frequency and baseband filtering.

Interference from another transmitter using the same frequency, common in cellular reuse plans and broadcast single-frequency networks, and not removable by receiver filtering.

The ratio in decibels of wanted carrier power to total interference power at the receiver, determining whether demodulation meets its required quality threshold.

The ratio of wanted signal power to noise power at a given point, expressed in decibels; it sets the achievable error rate for a given modulation and coding scheme.

The fraction of received bits that are incorrect, a fundamental quality measure of a digital link that depends on signal-to-noise ratio, modulation and coding.

Energy per information bit divided by noise power spectral density; a bandwidth-independent measure of digital link quality used to compare modulation and coding schemes.

Distortion in which energy from one symbol smears into neighbouring symbol intervals due to channel dispersion or band limiting, raising the error rate.

The condition for zero intersymbol interference at symbol instants: the overall pulse shape must be zero at all other sampling instants, satisfied by raised-cosine filtering.

A receive filter whose impulse response mirrors the transmitted pulse, maximising signal-to-noise ratio at the sampling instant in the presence of white noise.

A multicarrier modulation that splits data across many closely spaced orthogonal subcarriers, enabling simple equalisation and high spectral efficiency in dispersive channels.

A guard interval formed by copying the end of an OFDM symbol to its start, which absorbs multipath echoes and preserves subcarrier orthogonality.

The ratio of peak envelope power to average power of a signal; high values stress transmitter amplifiers and demand linear operation to avoid spectral regrowth.

Widening of a transmitted signal's occupied bandwidth caused by nonlinear amplification, producing out-of-band emissions that can interfere with neighbouring channels.

Any unwanted emission outside the necessary bandwidth, including harmonics and mixer products, subject to regulatory limits because it can disturb other radio services.

A calculation summing transmit power, gains, and all losses and noise contributions to predict received signal level and margin against the required threshold.