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Topic: Tropospheric ducting

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	Tropospheric DX Modes
		Ducting conditions usually vary over short time periods as opposed to enhancement which is more stable.
		Ducts located behind cold fronts ("post-frontal ducts") are notoriously unstable as paths can even be interrupted by things such as heavy rain showers associated with the cold front itself.
		Frequencies affected by ducting are determined by the vertical thickness of an inversion.
	home.cogeco.ca /~vem3ont22/propagation/tr-modes.htm (1449 words)

	TV-FM DX at AllExperts
		Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet (7,620 meters).
		Tropospheric ducting is a type of radio propagation that tends to happen during periods of stable, anticyclonic weather.
		Tropospheric ducting of UHF television signals is relatively common during the summer and autumn months, and is the result of change in the refractive index of the atmosphere at the boundary between air masses of different temperatures and humidities.
	en.allexperts.com /e/t/tv/tv-fm_dx.htm (5408 words)

	TV-FM DX - Wikipedia, the free encyclopedia
		Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet (7,620 meters).
		Tropospheric ducting is a type of radio propagation that tends to happen during periods of stable, anticyclonic weather.
		Tropospheric ducting of UHF television signals is relatively common during the summer and autumn months, and is the result of change in the refractive index of the atmosphere at the boundary between air masses of different temperatures and humidities.
	en.wikipedia.org /wiki/Tropospheric_ducting (5344 words)

	Tropospheric Ducting Forecast for VHF & UHF Radio & TV
		Tropospheric Ducting Forecast for VHF and UHF Radio and TV William Hepburn's
		The areas noted in the forecast have the necessary atmospheric conditions to produce tropospheric bending of VHF, UHF and/or microwave radio waves.
		Tropospheric bending extends the range of radio and TV stations well beyond their normal limit and thus increases interference amongst stations as well.
	www.dxinfocentre.com /tropo.html (156 words)

	VHF/UHF RADIO DUCTING IN AUSTRALIA'S SOUTH
		The Duct information presented here is mainly derived from paths across southern Australia, especially across to Adelaide and beyond to the Great Australian Bight path, which can stretch from one side of the country to the other in an east west direction at around 3000 km.
		A Duct is usually a layer of warmer air, with less humidity, in comparison to the air above and below it, which can cover, like a blanket, the whole of a HIGH pressure cell (depending upon fronts and weather conditions around the High cell).
		A Duct or Trapping layer is great strengthening of a Superrefractive layer, to the extent where the signal is curved enough in the layer to then be directed at the lower edge of the layer at a very small angle.
	www.users.bigpond.com /vk2krr/DUCTING.htm (3045 words)

	Is TV like radio w/ a night time effect? [Archive] - SatelliteGuys.US
		Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet.
		Tropospheric ducting is a type of radio propagation that tends to happen during periods of stable, anti-cyclonic weather.
		Tropospheric ducting over water, particularly between California and Hawaii, Brazil and Africa, Australia and New Zealand, Australia and Indonesia, and Bahrain and Pakistan, has produced VHF/UHF reception ranging from 1,000 to 3,000 miles (4,500 km).
	www.satelliteguys.us /archive/index.php/t-63544.html (1079 words)

	Tropospheric propagation
		At times signals may even be trapped in an elevated duct in a form of radio signal propagation known as tropospheric ducting.
		These elevated tropospheric ducts occur when a mass of air with a high refractive index has a mass of air with a lower refractive index underneath and above it as a result of the movement of air that can occur under some conditions.
		Tropospheric radio propagation effects occur comparatively close to the surface of the Earth.
	www.g1ksw.co.uk /tropoprop.htm (1411 words)

	The USS Liberty Inquiry Forum - View Single Post - Refusal to deal with: Radar (Site not responding. Last check: 2007-10-16)
		Below are a few quotes, from various sources, that indicate tropospheric ducting in the Mediterrain Sea region, during summer months, is a common occurrence.
		[Tropospheric ducting] contacts of 1000 km (620 mi) have been made on all bands through 10 GHz in the US and over 1600 km (1000 mi) across the Mediterranean Sea.
		Generally, tropospheric ducting or reflection occurs frequently when there are sharp changes of temperatures of different air masses, with microscopic water droplets condensing between these air layers forming a mirror for VHF RF on their borders.
	www.usslibertyinquiry.com /forums/showpost.php?p=1880&postcount=7 (349 words)

	Tropospheric ducting Information - tropospheric ducting forecast
		In this propagation tropospheric ducting forecast method, when the signal encounters a rise in temperature in the atmosphere instead of the normal decrease (known as a temperature inversion), the higher refractive index of the atmosphere there will cause the signal to be bent.
		Tropospheric ducting over water, particularly between California and Hawaii, Brazil and Africa, Australia and New Zealand, Australia and Indonesia, and Bahrain and Pakistan, tropospheric ducting has produced VHF/UHF reception ranging from 1,000 to 3,000 miles (1,600–4,800 km).
		Consequently an incident television or radio signal is capable of being reflected up to distances approaching uhf tropospheric ducting forecast that of conventional Sporadic E propagation.
	www.inanot.com /Ina-Electronics_Topics_T-/Tropospheric_ducting.html (5054 words)

	Tropospheric Ducting
		In conditions of tropospheric ducting however, it is possible to contact stations that you do not have line of sight with.
		Tropospheric ducting is quite a rare happening in the Chicagoland area.
		Ducting occurs when humidity and temperature create another "wall" of ionized particles in the troposphere.
	www.qsl.net /kc9dam/tropo.html (449 words)

	DF5AI.NET - Amateur Radio Propagation Studies
		Tropospheric ducting not only attracts the interest of VHF radio amateurs but also of engineers designing, for example, microwave links for commercial purposes.
		In a detailed paper, Andrew summarizes the obervational characteristics of tropospheric ducting of radiowaves, explains the findings of the SODAR measurements, provides an introduction to the theory and, finally, assembles a consistent picture about the myths and facts in tropospheric duct propagation.
		"Ducts act more like a boundary layer by repeatedly refracting VHF and UHF signals resulting in long distance propagation" and, in consequence, tropospheric ducts do not act as a high-pass filter in accordance to the waveguide theory but as a band-pass filter.
	www.df5ai.net (1557 words)

	[No title] (Site not responding. Last check: 2007-10-16)
		Durring a duct it is possible to hear stations on your scanner in the VHF and UHF band from about 50 to 900 mhz that includes picking up stations hundreds of miles away from your local police to fm radio to tv.
		The key word hear is "ducting" in your house you use ducts to shuffle warm and cool air around the house.
		Tropospheric ducting occurs mostly in the warm weather months of the summer and sometimes in the presence of large storm systems.
	www.angelfire.com /sc/scannerpost/tropo.html (388 words)

	VHF Signal Propagation (Site not responding. Last check: 2007-10-16)
		Tropospheric Enhancements - Within the broad classification of tropospheric enhancement, there are several different and distinct propagation modes that make it possible for FM and TV signals to travel far greater distances than the normal radio line-of-sight horizon.
		Tropospheric scatter at FM and TV frequencies is caused when the paths of radio signals are altered by slight changes in the refractive index in the lower atmosphere caused by air turbulence, and small changes in temperature, humidity and barometric pressure.
		Ducted signals are typically quite strong, sometimes so strong that they can cause interference to local signals on the same frequency.
	dxfm.com /Content/propagation.htm (5763 words)

	[No title] (Site not responding. Last check: 2007-10-16)
		The skip distance is the distance from the end of the ground wave to the point at which the sky wave is refracted back to earth Space waves travel in contact with the earth’s surface.
		In tropospheric ducting the refracted wave travels back and strike the earth.
		Tropospheric ducting causes the waves to reach great distances following the earth’s curvature.
	www.alsirhan.com /pub/Tr243/Rev4.doc (285 words)

	Articles on VHF tropospheric radio propagation
		Intense tropospheric inversion layers may result in the ducting of radiowaves which enables long distance radio propagation in VHF, UHF and SHF too.
		Between the northwest of Spain and the Canary Islands, intense inversion layers are found between 1000m and 2000m altitude indicating significant discontinuities in air temperature and, in particular, in air humidity.
		Tropospheric dx QSOs exceeding the distance of 3.000 kilometers must be considered a true rarity in amateur radio.
	df5ai.net /Material/articles3.html (1021 words)

	The Joy FM
		Ducting takes place when refraction is so great that radio waves are bent back to the surface of the Earth.
		When tropospheric ducting conditions exist over a wide geographic area, signals may remain very strong over distances of 900 miles or more.
		Ducting results from the gradient created by a sharp increase in temperature with altitude, quite the opposite of normal atmospheric conditions.
	thejoyfm.com /Home.aspx?NEWS_ID=59 (754 words)

	Tropospheric Ducting :: PMR446 Personal Mobile Radio (Site not responding. Last check: 2007-10-16)
		Tropospheric conditions are looking quite good for this Sunday 6th April...
		The troposphere, an area of atmospheric regions close to the Earth, causes radio waves travelling within it to bend and thereby return to Earth at points beyond the horizon allowing you to make contact with other radio stations at a greater distance than normally possible.
		This area, between the ground and the mass of warm air is known as a duct.
	www.446user.co.uk /article_33.html (477 words)

	Tropospheric Ducting
		If you find that NCPR has disappeared, and some other station is coming in instead—you may be experiencing the results of a process known technically as tropospheric ducting, caused when a layer of cold air traps a layer of warm air near the ground over a wide area.
		Our listeners have heard from stations as far away as Iowa and Minnesota (and their listeners have heard us).
		This has been an alert from Radio Bob.
	www.northcountrypublicradio.org /ducting.html (89 words)

	Articles on VHF tropospheric radio propagation
		Intense tropospheric inversion layers may result in the ducting of radiowaves which enables long distance radio propagation in VHF, UHF and SHF too.
		Between the northwest of Spain and the Canary Islands, intense inversion layers are found between 1000m and 2000m altitude indicating significant discontinuities in air temperature and, in particular, in air humidity.
		Tropospheric dx QSOs exceeding the distance of 3.000 kilometers must be considered a true rarity in amateur radio.
	www.df5ai.net /Material/articles3.html (1021 words)

	V/UHF Tropospheric Ducting Forecast (Site not responding. Last check: 2007-10-16)
		It is an experimental forecast of distant VHF and UHF propagation via the mode called "Tropospheric Ducting".
		The areas noted in the forecast have the necessary atmospheric conditions to produce tropospheric bending of UHF or VHF TV and radio waves.
		Tropospheric bending extends the range of stations well beyond their normal limit.
	duxpond.com /weather/TroposphericDucting.html (167 words)

	The Joy FM
		Ducting takes place when refraction is so great that radio waves are bent back to the surface of the Earth.
		When tropospheric ducting conditions exist over a wide geographic area, signals may remain very strong over distances of 900 miles or more.
		Ducting results from the gradient created by a sharp increase in temperature with altitude, quite the opposite of normal atmospheric conditions.
	www.thejoyfm.com /Home.aspx?NEWS_ID=59 (744 words)

	Television interference (Co-channel reception) - Wikipedia, the free encyclopedia
		This is caused by the signals from two different TV transmitters (operating on the same frequency) arriving at the aerial input of the TV.
		This can be caused by tropospheric ducting (also known as Tropospheric scatter) which occurs during high pressure weather conditions.
		This is a diagram showing how a reflective situation such as sporadic E or a tropospheric duct can allow distant signals to travel to RX from the distant transmitter
	en.wikipedia.org /wiki/Television_interference_(Co-channel_reception) (215 words)

	cars - TV/FM DX
		However, because of a phenomenon known as tropospheric scatter, television and radio signals are received at a relatively short distance beyond the optical horizon at reduced signal strengths.
		In certain parts of the world, notably the Mediterranean and the Arabian Gulf, tropospheric ducting conditions can become established for many months of the year to the extent that viewers receive regular quality reception of television signals over distances up to around 1,000 miles.
		Tropospheric signals exhibit a slow cycle of fading and will occasionally produce signals sufficiently strong for noise-free stereo reception on FM or noise-free TV pictures, sometimes in full color.
	www.carluvers.com /cars/E-skip (3960 words)

	Scanner frequencies, police, fire, NASCAR, airport, Ham radio.
		TV DXing and FM DXing are similar in that they both typically involve receiving distant signals via tropospheric ducting and sporadic E-skip.
		Tropospheric ducting occurs when a particular combination of temperature and humidity create a layer, or barrier, of ionized particles in the troposphere.
		Television signals can travel along a tropospheric duct for hundreds of miles until the signals escape the duct and return to the earth's surface.
	www.nationalradiodata.com /resources-tv-dxing.html (228 words)

	UHF TV-DX and fringe reception techniques
		Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 25,000 feet.
		Tropospheric ducting over water, particularly between California and Hawaii, Brazil and Africa, Australia and New Zealand, Australia and Indonesia, and Bahrain and Pakistan, has produced UHF reception ranging from 1,000 to 3,000 miles (4,500 km).
		The theoretical maximum distance that can be worked by tropospheric scatter is limited ultimately by the line of sight distance between the TV transmitter and receiving station have of the same scattering region of the troposphere.
	www.geocities.com /toddemslie/UHF-TV-DX.html (4954 words)

	Hamquick Technician Class Tutorials (Site not responding. Last check: 2007-10-16)
		Tropospheric ducting or ('tropo' for short) is a special type of radio wave propagation which occurs in the VHF and UHF frequency range.
		Another important fact to consider is that signal losses or path loss through the troposphere increases as the frequency increases.
		This is an amazing part of amateur radio communications where hams direct their powerful signals toward the moon and attempt to contact fellow hams across the world with their moon-echoes.
	www.hamquick.com /tutorial_index.php?id=17 (533 words)

	Radio Ducting
		Tropospheric ducting occurs when we get a sharp rate of change in the dielectric constant as we move upwards through the atmosphere.
		If we look at a vertical profile of the atmosphere showing ducting potential, we can see that there is a sharp increase in temperature (an inversion), coupled with a sharp fall in dew-point (indicating a fall in humidity).
		To decide wether there may be potential for ducting then first consult the Met Office forecast synoptic charts.
	homepage.ntlworld.com /colin.martin5/radio/ducting.html (692 words)

	The USS Liberty Inquiry Forum - Refusal to deal with: Radar (Site not responding. Last check: 2007-10-16)
		Sunspot activity and tropospheric ducting are mutually exclusive phenomena.
		Of course, sunspot activity does not affect tropospheric ducting; thus, it's possible that long-distance propagation for VHF and UHF communications and RADAR signals may have occurred via tropo-ducting or tropo-scattering.
		Assuming no ducting whatsoever, that means that even to the naked eye (or certainly someone with binoculars) would see Liberty hull down at 60 miles.
	www.usslibertyinquiry.com /forums/printthread.php?t=307&pp=40 (6116 words)

	C. Crane Company - Quiet Before the Storm, Distant Radio Sounds After (Site not responding. Last check: 2007-10-16)
		The combination of an increase in humidity and a decrease in temperature at the surface results in a phenomenon called tropospheric ducting.
		It's called tropospheric, because the ducting occurs in the troposphere, the lowest of the three layers of the earth's atmosphere (which also includes the stratosphere, the middle layer, which holds little water vapor and has little affect on radio waves, and the ionosphere, the top layer, which is used for long-distance radio wave propagation).
		In addition to ducting, recent rains also increase soil conductivity in a lot of areas.
	www.ccrane.com /library/distant-radio.08.20.01.aspx (1119 words)

	TVTechnology - RF Technology
		Changing the Longley-Rice parameters for each interference analysis to accurately represent the specific climate and tropospheric weather for each path would, of course, be extremely difficult.
		Tropospheric ducting occurs due to subsidence, frontal or advection inversions.
		If you are interested in learning more about tropospheric propagation, I found a Web site that offers forecasts on the location and strength of inversions and ducting that lead to enhanced propagation.
	www.tvtechnology.com /features/On-RF/f-DL-signals.shtml (1695 words)

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