A thermal fade is a phenomenon of
wireless
Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or other continuous guided transm ...
signal degradation (
fading
In wireless communications, fading is the variation of signal attenuation over variables like time, geographical position, and radio frequency. Fading is often modeled as a random process. In wireless systems, fading may either be due to mul ...
) caused by temperature and relative
humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...
factors. As the prevailing environmental conditions change (e.g., from hot to cool, humid to
arid
Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.Perez-Aguilar, L. Y., Plata ...
, or
day to night), the
electromagnetic wave
In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ...
s
refract
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenome ...
differently, thus altering the power distribution and possibly the direction of the signal. This is the same process that causes
visible light
Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
to "bend" over a
heated road or other surfaces on hot days.
Thermal fade primarily affects
very
Very may refer to:
* English's prevailing intensifier
Businesses
* The Very Group
The Very Group Limited is a multi-brand online retailer and financial services provider in the United Kingdom and Ireland. Its head offices are based in the ...
and
ultra high frequencies, regardless of
modulation
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information.
The process encodes information in form of the modulation or message ...
method (
AM,
FM, etc.). The thermal fade margin is calculated from subtracting losses from antenna gains. A higher
fade margin is required in humid locations, and lower in dry ones.
See also
*
Atmospheric duct
*
Refractive index
In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...
*
Thermal degradation of polymers - sometimes referred to as "thermal fade".
Radio frequency propagation fading
References
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