Random (temporary) disappearance of the received signal for a given frequency according to the time and/or the location.

Fast fading

1) Signal fading due to movement of the station in a very diversified area (during the multipath propagation). 2) Fading arising when the coherence time of the channel is small relative to the delay constraint of the channel.


Transmission line (e.g. wire or waveguide) connecting the antenna with the transmitter output or the receiver input.

First Fresnel zone

Fresnel zone situated close to the axis, within which propagates the greatest part of the energy of an electromagnetic wave. The first zone is the most important in the radio transmission and is unlikely to be obstructed by objects located along the radio path.

Fixed service

A radiocommunication service between specified fixed points.

Fixed-saellite service

A radiocommunication service between earth stations at given positions, when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite-to-satellite links, which may also be operated in the inter-satellite service; the fixed-satellite service may also include feeder links for other space radiocommunication services.

Flat channel

Radio channel, in which occurs flat fading.

Free space

A theoretical concept of space devoid of all matter. Free space also implies remoteness from material objects that could influence the propagation of electromagnetic waves.

Free space loss

1) Decrease in signal strength that occurs when an electromagnetic wave travels over a line of sight path in free space. 2) The signal attenuation that would result if all absorbing, diffracting, obstructing, refracting, scattering, and reflecting influences (of environment) were sufficiently removed so as to have no effect on propagation.

Free space propagation

1) Propagation of radio waves in remoteness from material objects that could influence on the electromagnetic waves propagation. 2) Hypothetic propagation in the space devoid of all matter


W służbach radiowych termin "częstotliwość" potocznie rozumiany jest czasem jako "kanał częstotliwościowy o znanej częstotliwości środkowej".


Term of a certain range frequencies without a clear indication of the frequency limits, such as "core band" or band with number-letter mark. This term is also used in the sense of the term bandwidth.

Frequency Allocation Table

Table, in which radio spectrum is divided into sub-bands. For each of the frequency subbands the one or more radiocommunication services are allocated.

Frequency band

Term of a certain range frequencies without a clear indication of the frequency limits, such as "core band" or band with number-letter mark. This term is also used in the sense of the term bandwidth.

Frequency band

Continuous range of frequencies extending between two limiting frequencies. Frequency band is defined by giving two numerical values explicitly defining the corresponding range, meaning the frequency limits.

Frequency block

A group of frequencies (contiguous portion of spectrum) separated from a specific frequency band or a sub-band for the purpose of carrying one or more radio channels (usually assigned to use by single operator).

Frequency channel

Part of the radio spectrum intended to be used for a signal transmission through the transmission channel.

Frequency deviation

Parameter of angle modulated signal interpreted as maximum instantaneous difference between a momentary frequency and the nominal carrier frequency.

Frequency guard band

A frequency band deliberately left vacant between two channels or frequency bands to provide an adequate margin of safety in case of mutual interference.

Frequency selective fading

Fading exists in the channel, in which the coherence bandwidth is smaller than the bandwidth of the signal. Different frequency components of the signal therefore experience decorrelated fading.

Frequency sharing

The assignment to or use of the same radio frequency by two or more stations that are separated geographically or that use the frequency at different times.

Fresnel zone

The annular area of the spherical surface of a radio wavefront, whose boundaries are defined distances dependent on the length of the radio path and multiples of half the wavelength. Number of Fresnel zones is theoretically infinite. Are positioned concentrically in relation to an axis which is straight between transmitting and receiving points.