A skip zone, also called a silent zone or zone of silence, is a region where a radio transmission can not be received. The zone is located between regions both closer and farther from the transmitter where reception is possible.
Cause
When using medium to high-frequency radio
telecommunication
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
, there are
radio wave
Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...
s which travel both parallel to the ground, and towards the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
, referred to as a
ground wave
Ground wave is a mode of radio propagation that consists of currents traveling through the earth. Ground waves propagate parallel to and adjacent to the surface of the Earth, and are capable of covering long distances by diffracting around the E ...
and
sky wave, respectively. A skip zone is an annular region between the farthest points at which the ground wave can be received and the nearest point at which the refracted sky waves can be received. Within this region, no signal can be received because, due to the conditions of the local ionosphere, the relevant sky waves are not reflected but penetrate the ionosphere.
The skip zone is a
natural phenomenon
A natural phenomenon is an observable event which is not man-made. Examples include: sunrise, weather, fog, thunder, tornadoes; biological processes, decomposition, germination; physical processes, wave propagation, erosion; tidal flow, and na ...
that cannot be influenced by technical means. Its width depends on the height and shape of the ionosphere and, particularly, on the local ionospheric maximum electron density characterized by critical frequency f
oF
2. It varies mainly with this parameter, being larger for low f
oF
2. With a fixed working frequency it is large by night and may even disappear by day. Transmitting at night is most effective for long-distance communication but the skip zone becomes significantly larger.
Very high frequency waves and higher normally travel through the ionosphere wherefore communication via skywave is exceptional. A highly ionized Es-Layer that occasionally may appear in summer may produce such
Sporadic E propagation.
Avoidance
A method of decreasing the skip zone is by decreasing the frequency of the radio waves. Decreasing the frequency is akin to increasing the ionospheric width. A point is eventually reached when decreasing the frequency results in a zero distance skip zone. In other words, a frequency exists for which vertically incident radio waves will always be refracted back to the Earth. This frequency is equivalent to the ionospheric plasma frequency and is also known as the ionospheric critical frequency, or f
oF
2.
Other
Skip zone is the subject of a film 'SKIPZONE' made in 1992 by UK artist,
Peter Lee-Jones. It refers to areas in Scottish Highlands where it is difficult to obtain radio and TV reception.
In the episode "Short Wave"
of ''
Father Knows Best
''Father Knows Best'' is an American sitcom starring Robert Young (actor), Robert Young, Jane Wyatt, Elinor Donahue, Billy Gray (actor), Billy Gray and Lauren Chapin. The series, which began on radio in 1949, aired as a television show for six ...
'', the family hears a distress call from a small boat at sea. Jim explains that the reason they, and not the Coast Guard, can hear the transmission is because of a "skip".
See also
*
Shortwave
Shortwave radio is radio transmission using radio frequencies in the shortwave bands (SW). There is no official definition of the band range, but it always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (app ...
References
Sources
*{{FS1037C MS188
Radio frequency propagation