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Tropospheric propagation

March 14, 2023

Tropospheric propagation describes electromagnetic propagation in relation to the troposphere. The service area from a VHF or UHF radio transmitter extends to just beyond the optical horizon, at which point signals start to rapidly reduce in strength. Viewers living in such a "deep fringe" reception area will notice that during certain conditions, weak signals normally masked by noise increase in signal strength to allow quality reception. Such conditions are related to the current state of the troposphere.

Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 7.5 km. Such signals are thus directly affected by weather conditions extending over hundreds of kilometres. During very settled, warm anticyclonic weather (i.e., high pressure), usually weak signals from distant transmitters improve in strength. Another symptom during such conditions may be interference to the local transmitter resulting in co-channel interference, usually horizontal lines or an extra floating picture with analog broadcasts and break-up with digital broadcasts. A settled high-pressure system gives the characteristic conditions for enhanced tropospheric propagation, in particular favouring signals which travel along the prevailing isobar pattern (rather than across it). Such weather conditions can occur at any time, but generally the summer and autumn months are the best periods. In certain favourable locations, enhanced tropospheric propagation may enable reception of ultra high frequency (UHF) TV signals up to 1 600 km or more.

The observable characteristics of such high-pressure systems are usually clear, cloudless days with little or no wind. At sunset the upper air cools, as does the surface temperature, but at different rates. This produces a boundary or temperature gradient, which allows an inversion level to form – a similar effect occurs at sunrise. The inversion is capable of allowing very high frequency (VHF) and UHF signal propagation well beyond the normal radio horizon distance.

The inversion effectively reduces sky wave radiation from a transmitter – normally VHF and UHF signals travel on into space when they reach the horizon, the refractive index of the ionosphere preventing signal return. With temperature inversion, however, the signal is to a large extent refracted over the horizon rather than continuing along a direct path into outer space.

Fog also produces good tropospheric results, again due to inversion effects. Fog occurs during high-pressure weather, and if such conditions result in a large belt of fog with clear sky above, there will be heating of the upper fog level and thus an inversion. This situation often arises towards night fall, continues overnight and clears with the sunrise over a period of around 4 to 5 hours.

Tropospheric ducting

Main article: Atmospheric ducting

Tropospheric ducting is a type of radio propagation that tends to happen during periods of stable, anticyclonic weather. In this propagation 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 affects all frequencies, and enhanced signals tend to travel up to 1 300 km (though some people have received tropospheric ducting beyond 1 600 km), while with tropospheric-bending, stable signals with good signal strength from 800 km away are not uncommon when the refractive index of the atmosphere is fairly high.

Tropospheric ducting of radio and 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. Using an analogy, it can be said that the denser air at ground level slows the wave front a little more than does the rare upper air, imparting a downward curve to the wave travel.

Ducting can occur on a very large scale when a large mass of cold air is overrun by warm air. This is termed a temperature inversion, and the boundary between the two air masses may extend for 1 600 km or more along a stationary weather front.

Temperature inversions occur most frequently along coastal areas bordering large bodies of water. This is the result of natural onshore movement of cool, humid air shortly after sunset when the ground air cools more quickly than the upper air layers. The same action may take place in the morning when the rising sun warms the upper layers.

Even though tropospheric ducting has been occasionally observed down to 40 MHz, the signal levels are usually very weak. Higher frequencies above 90 MHz are generally more favourably propagated.

High mountainous areas and undulating terrain between the transmitter and receiver can form an effective barrier to tropospheric signals. Ideally, a relatively flat land path between the transmitter and receiver is ideal for tropospheric ducting. Sea paths also tend to produce superior results.

In certain parts of the world, notably the Mediterranean Sea and the Persian Gulf, tropospheric ducting conditions can become established for many months of the year to the extent that viewers regularly receive quality reception of signals over distances of 1 600 km. Such conditions are normally optimum during very hot settled summer weather.

Tropospheric ducting over water, particularly between California and Hawaii, Brazil and Africa, Australia and New Zealand, Australia and Indonesia, Strait of Florida, and Bahrain and Pakistan, has produced VHF/UHF reception ranging from 1 600 to 4 800 km. A US listening post was built in Ethiopia to exploit a common ducting of signals from southern Russia.

Tropospheric signals exhibit a slow cycle of fading and will occasionally produce signals sufficiently strong for noise-free stereophonic sound, reception of the Radio Data System (RDS), HD Radio streams on FM, noise-free, colour TV pictures, or stable DTV reception, as well stable DAB Radio reception. With DVB-T, it can also enable a wide single-frequency network, as long as the two transmitters are within a guard interval and are almost equidistant from the receiver as well as synchronised. However, if they are not synchronised and equidistant, they will interfere with each other.

Virtually all long-distance reception of digital television occurs by tropospheric ducting (due to most TV stations broadcasting in the ultra high frequency band).

Notable and record distance tropospheric DX receptions

"DXing is the art and science of listening to distant stations (D=distance X=xmitter or transmitter)."[1] The ARRL, association for amateur radio maintains the list of North American distance records, which includes tropo results.

  • On October 18, 1975, Rijn Muntjewerff, the Netherlands, received UHF channel E34 Pajala, Sweden, at a distance of 1,150 miles (1,851 km).[2]
  • On June 13, 1989, Shel Remington, Keaau, Hawaii, received several 88–108 MHz FM signals from Tijuana, Mexico, at a distance of 2,536 miles (4,081 km).[3]
  • Throughout the 1990s, Fernando Garcia, located at what could be considered an ideal tropospheric DX location near Monterrey, Mexico, received numerous 1,000+ mile (1,600+ km) stations via tropospheric propagation, both over the Gulf of Mexico and past land. Among his receptions are WGNT-27 from Portsmouth, Virginia, at a distance of 1,608 miles (2,588 km) and low-power (LPTV) station W38BB from Raleigh, North Carolina, at a distance of 1,460 miles (2,350 km)[4]
  • On May 11, 2003, Jeff Kruszka, living in south Louisiana, received a few UHF DTV signals from 800+ miles. The longest of these was WNCN-DT, channel 55, Goldsboro, North Carolina, at a distance of 835 miles (1,344 km) (at the time, the record for UHF DTV).[5]
  • On December 9, 2004, Polish DXer Maciej Ługowski received "Five" TV station on UHF ch.37 from London-Croydon transmitter and BBC2 UHF ch.46 from Bluebell Hill transmitter near Warsaw, Poland at 1,466 kilometres (911 mi) and 1,427 kilometres (887 mi), respectively.[6]
  • On October 15, 2006, a German DXer known on YouTube as EifelDX received the Norge Mux on channel E58, transmitter Oslo, with a distance of 1,085 kilometres (674 mi).[7]
  • On the late evening of June 19, 2007 and into the early morning hours of June 20, 2007, three DXers in eastern Massachusetts, Jeff Lehmann, Keith McGinnis, and Roy Barstow, received FM signals from southern Florida via tropo. All three logged WEAT 104.3 West Palm Beach, Florida, and WRMF 97.9 Palm Beach, Florida, at distances of around 1,200 miles (1,931 km), and Barstow logged WHDR 93.1 Miami, Florida, at a distance of 1,210 miles (1,947 km).[8]
  • On December 17, 2007, Polish DXer Maciej Ługowski received BBC Radio Scotland on 93,7 MHz from Keelylang Hill (Orkney Islands) transmitter near Warsaw, Poland at 1,706 km (1,060 mi) distance. BBC Scotland reception continued for next two days.[9][10]
  • On November 3, 2008, Swedish Radio Amateur Kjell Jarl SM7GVF contacted Russian Radio Amateur RA6HHT
    at a distance of 2,315 km (1,438 mi) on 144Mhz.[11]
  • On April 23, 2009, a San Antonio-area DXer received WFTS-TV 28's digital signal from Tampa, Florida, at a distance of 995 miles (1,601 km).[12]
  • On the late evening of August 24 into the afternoon of August 25, 2009, a DX'er in Burnt River, Ontario, Canada, received several FM radio stations via tropo from Arkansas, Illinois, Iowa, Kansas, Michigan, Missouri, Ohio, Oklahoma, Pennsylvania, and Wisconsin.[13]
  • On September 28, 2016, European tropospheric FM DX record was newly set by Jürgen Bartels in Süllwarden, Northern Germany who received Spanish station RNE5TN on 93.7 MHz from Santiago de Compostela/Monte Pedroso transmitter at 1,715 km (1,066 mi) distance.[14]
  • On September 27 and 28, 2017 various DXers in northeastern Europe observed extreme ducting in VHF broadcast band. Top distance was achieved by Łukasz K. in Tomaszów Mazowiecki, Poland, who reported signals from Kolari transmitter, northern Finland at 1,798 km (1,117 mi).[15]
  • On October 10, 2018, Ukrainian DXer Vladimir Doroshenko (MrVlaDor) received a signal from Danish transmitter Holstebro/Mejrup in Dnipro at a distance of 1,960 km (1,220 mi).[16] It sets the new tropo FM DX record for Europe. At the same time, FM DXers in Poland received FM radiostations from Moscow for the first time via troposphere at distances 1,100 kilometres (684 mi) – 1,300 kilometres (808 mi).
  • On November 2, 2020, Maltese based Param DXer, received FM stations from the Valencia region across the Mediterranean in early morning due to extreme tropo ducting. The distance accounts for around 1,365 kilometres (848 miles). It is exceptionally rare that such signals made their way to the island despite being out of the tropo season.

See also

References

  1. ^ "DXing.com – The Web Resource for Radio Hobbyists". Universal Radio Research. November 2, 2016. Retrieved November 12, 2016.
  2. ^ "Rijn Muntjewerff's TV DX Netherlands 1961–2005". Todd Emslie's TV DX Page. Todd Emslie. Retrieved November 12, 2016.
  3. ^ "WTFDA FM ALL-TIME DISTANCE RECORDS – AS OF 2/1/16". WTFDA.org (Worldwide TV-FM DX Association). February 1, 2016. Retrieved November 12, 2016. ()
  4. ^ "FERNANDO GARCIA: North America's champion of tropo TV DX". THE TV DX EXPOSITION. Retrieved November 12, 2016.
  5. ^ "JEFF KRUSZKA'S RECORD-BREAKING DTV TROPO as received in south Louisiana". THE TV DX EXPOSITION. Retrieved November 12, 2016.
  6. ^ Emel. "XPLORADIO: 9.12.2004 – gigantyczne tropo UHF i FM!". XPLORADIO. Retrieved 2018-07-01.
  7. ^ https://youtube.com/cPsi0GPeiXc[dead link]
  8. ^ "TROPO MA to FL!!!! 97.9 WRMF". Worldwide TV-FM DX Association; WTFDA Forums. June 2007. Retrieved November 12, 2016. ()
  9. ^ "My FM-DX Records". XPLORADIO. Maciej Ługowski. Retrieved 2018-07-01.
  10. ^ EMEL DX (2011-09-19), FM DX: 1700 KM TROPO!, archived from the original on 2021-12-20, retrieved 2017-10-10
  11. ^ "Kjell, SM7GVF (ex SM4GVF) – Best DX worked by SM7GVF from JO77GA". Retrieved November 12, 2016.
  12. ^ "WA5IYX DTV DX Screen Captures". Retrieved November 12, 2016.
  13. ^ "Aug 24–25 2009 Es (er, Tropo)". Worldwide TV-FM DX Association; WTFDA Forums. August 2009. Retrieved November 12, 2016. ()
  14. ^ https://www.fmlist.org/fm_logmapt.php?datum=2016-09-28&band=Tropo&target=ALL&rxin=ALL ()
  15. ^ "FM DX Tropo Log – Tomaszów Mazowiecki, Poland".
  16. ^ Archived at Ghostarchive and the : "[Tropo] 98.5 – DR P4 – Holstebro/Mejrup, Denmark (1960 km)". YouTube.
  • "DXing FAQ". Worldwide TV-FM DX Association. Retrieved April 25, 2005.
  • "William Hepburn's VHF / UHF Tropospheric Ducting Forecast". William Hepburn's TV & Radio DX Information Centre. Retrieved June 12, 2006.
  • Tropospheric Ducting YouTube Channel of FMDXUA – [1]
  • . Matthew C. Sittel's DX Page. Archived from the original on September 27, 2007. Retrieved April 26, 2005.{{cite web}}: CS1 maint: unfit URL (link)
  • . Archived from the original on 2015-03-01. Retrieved 2015-03-02.oldtvguides.com

March 14, 2023
tropospheric, propagation, this, article, multiple, issues, please, help, improve, discuss, these, issues, talk, page, learn, when, remove, these, template, messages, this, article, uses, bare, urls, which, uninformative, vulnerable, link, please, consider, co. This article has multiple issues Please help improve it or discuss these issues on the talk page Learn how and when to remove these template messages This article uses bare URLs which are uninformative and vulnerable to link rot Please consider converting them to full citations to ensure the article remains verifiable and maintains a consistent citation style Several templates and tools are available to assist in formatting such as Reflinks documentation reFill documentation and Citation bot documentation August 2022 Learn how and when to remove this template message This article includes a list of general references but it lacks sufficient corresponding inline citations Please help to improve this article by introducing more precise citations April 2013 Learn how and when to remove this template message Learn how and when to remove this template message Tropospheric propagation describes electromagnetic propagation in relation to the troposphere The service area from a VHF or UHF radio transmitter extends to just beyond the optical horizon at which point signals start to rapidly reduce in strength Viewers living in such a deep fringe reception area will notice that during certain conditions weak signals normally masked by noise increase in signal strength to allow quality reception Such conditions are related to the current state of the troposphere Tropospheric propagated signals travel in the part of the atmosphere adjacent to the surface and extending to some 7 5 km Such signals are thus directly affected by weather conditions extending over hundreds of kilometres During very settled warm anticyclonic weather i e high pressure usually weak signals from distant transmitters improve in strength Another symptom during such conditions may be interference to the local transmitter resulting in co channel interference usually horizontal lines or an extra floating picture with analog broadcasts and break up with digital broadcasts A settled high pressure system gives the characteristic conditions for enhanced tropospheric propagation in particular favouring signals which travel along the prevailing isobar pattern rather than across it Such weather conditions can occur at any time but generally the summer and autumn months are the best periods In certain favourable locations enhanced tropospheric propagation may enable reception of ultra high frequency UHF TV signals up to 1 600 km or more The observable characteristics of such high pressure systems are usually clear cloudless days with little or no wind At sunset the upper air cools as does the surface temperature but at different rates This produces a boundary or temperature gradient which allows an inversion level to form a similar effect occurs at sunrise The inversion is capable of allowing very high frequency VHF and UHF signal propagation well beyond the normal radio horizon distance The inversion effectively reduces sky wave radiation from a transmitter normally VHF and UHF signals travel on into space when they reach the horizon the refractive index of the ionosphere preventing signal return With temperature inversion however the signal is to a large extent refracted over the horizon rather than continuing along a direct path into outer space Fog also produces good tropospheric results again due to inversion effects Fog occurs during high pressure weather and if such conditions result in a large belt of fog with clear sky above there will be heating of the upper fog level and thus an inversion This situation often arises towards night fall continues overnight and clears with the sunrise over a period of around 4 to 5 hours Contents 1 Tropospheric ducting 2 Notable and record distance tropospheric DX receptions 3 See also 4 ReferencesTropospheric ducting EditMain article Atmospheric ducting Tropospheric ducting is a type of radio propagation that tends to happen during periods of stable anticyclonic weather In this propagation 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 affects all frequencies and enhanced signals tend to travel up to 1 300 km though some people have received tropospheric ducting beyond 1 600 km while with tropospheric bending stable signals with good signal strength from 800 km away are not uncommon when the refractive index of the atmosphere is fairly high Tropospheric ducting of radio and 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 Using an analogy it can be said that the denser air at ground level slows the wave front a little more than does the rare upper air imparting a downward curve to the wave travel Ducting can occur on a very large scale when a large mass of cold air is overrun by warm air This is termed a temperature inversion and the boundary between the two air masses may extend for 1 600 km or more along a stationary weather front Temperature inversions occur most frequently along coastal areas bordering large bodies of water This is the result of natural onshore movement of cool humid air shortly after sunset when the ground air cools more quickly than the upper air layers The same action may take place in the morning when the rising sun warms the upper layers Even though tropospheric ducting has been occasionally observed down to 40 MHz the signal levels are usually very weak Higher frequencies above 90 MHz are generally more favourably propagated High mountainous areas and undulating terrain between the transmitter and receiver can form an effective barrier to tropospheric signals Ideally a relatively flat land path between the transmitter and receiver is ideal for tropospheric ducting Sea paths also tend to produce superior results In certain parts of the world notably the Mediterranean Sea and the Persian Gulf tropospheric ducting conditions can become established for many months of the year to the extent that viewers regularly receive quality reception of signals over distances of 1 600 km Such conditions are normally optimum during very hot settled summer weather Tropospheric ducting over water particularly between California and Hawaii Brazil and Africa Australia and New Zealand Australia and Indonesia Strait of Florida and Bahrain and Pakistan has produced VHF UHF reception ranging from 1 600 to 4 800 km A US listening post was built in Ethiopia to exploit a common ducting of signals from southern Russia Tropospheric signals exhibit a slow cycle of fading and will occasionally produce signals sufficiently strong for noise free stereophonic sound reception of the Radio Data System RDS HD Radio streams on FM noise free colour TV pictures or stable DTV reception as well stable DAB Radio reception With DVB T it can also enable a wide single frequency network as long as the two transmitters are within a guard interval and are almost equidistant from the receiver as well as synchronised However if they are not synchronised and equidistant they will interfere with each other Virtually all long distance reception of digital television occurs by tropospheric ducting due to most TV stations broadcasting in the ultra high frequency band Notable and record distance tropospheric DX receptions Edit DXing is the art and science of listening to distant stations D distance X xmitter or transmitter 1 The ARRL association for amateur radio maintains the list of North American distance records which includes tropo results On October 18 1975 Rijn Muntjewerff the Netherlands received UHF channel E34 Pajala Sweden at a distance of 1 150 miles 1 851 km 2 On June 13 1989 Shel Remington Keaau Hawaii received several 88 108 MHz FM signals from Tijuana Mexico at a distance of 2 536 miles 4 081 km 3 Throughout the 1990s Fernando Garcia located at what could be considered an ideal tropospheric DX location near Monterrey Mexico received numerous 1 000 mile 1 600 km stations via tropospheric propagation both over the Gulf of Mexico and past land Among his receptions are WGNT 27 from Portsmouth Virginia at a distance of 1 608 miles 2 588 km and low power LPTV station W38BB from Raleigh North Carolina at a distance of 1 460 miles 2 350 km 4 On May 11 2003 Jeff Kruszka living in south Louisiana received a few UHF DTV signals from 800 miles The longest of these was WNCN DT channel 55 Goldsboro North Carolina at a distance of 835 miles 1 344 km at the time the record for UHF DTV 5 On December 9 2004 Polish DXer Maciej Lugowski received Five TV station on UHF ch 37 from London Croydon transmitter and BBC2 UHF ch 46 from Bluebell Hill transmitter near Warsaw Poland at 1 466 kilometres 911 mi and 1 427 kilometres 887 mi respectively 6 On October 15 2006 a German DXer known on YouTube as EifelDX received the Norge Mux on channel E58 transmitter Oslo with a distance of 1 085 kilometres 674 mi 7 On the late evening of June 19 2007 and into the early morning hours of June 20 2007 three DXers in eastern Massachusetts Jeff Lehmann Keith McGinnis and Roy Barstow received FM signals from southern Florida via tropo All three logged WEAT 104 3 West Palm Beach Florida and WRMF 97 9 Palm Beach Florida at distances of around 1 200 miles 1 931 km and Barstow logged WHDR 93 1 Miami Florida at a distance of 1 210 miles 1 947 km 8 On December 17 2007 Polish DXer Maciej Lugowski received BBC Radio Scotland on 93 7 MHz from Keelylang Hill Orkney Islands transmitter near Warsaw Poland at 1 706 km 1 060 mi distance BBC Scotland reception continued for next two days 9 10 On November 3 2008 Swedish Radio Amateur Kjell Jarl SM7GVF contacted Russian Radio Amateur RA6HHTat a distance of 2 315 km 1 438 mi on 144Mhz 11 On April 23 2009 a San Antonio area DXer received WFTS TV 28 s digital signal from Tampa Florida at a distance of 995 miles 1 601 km 12 On the late evening of August 24 into the afternoon of August 25 2009 a DX er in Burnt River Ontario Canada received several FM radio stations via tropo from Arkansas Illinois Iowa Kansas Michigan Missouri Ohio Oklahoma Pennsylvania and Wisconsin 13 On September 28 2016 European tropospheric FM DX record was newly set by Jurgen Bartels in Sullwarden Northern Germany who received Spanish station RNE5TN on 93 7 MHz from Santiago de Compostela Monte Pedroso transmitter at 1 715 km 1 066 mi distance 14 On September 27 and 28 2017 various DXers in northeastern Europe observed extreme ducting in VHF broadcast band Top distance was achieved by Lukasz K in Tomaszow Mazowiecki Poland who reported signals from Kolari transmitter northern Finland at 1 798 km 1 117 mi 15 On October 10 2018 Ukrainian DXer Vladimir Doroshenko MrVlaDor received a signal from Danish transmitter Holstebro Mejrup in Dnipro at a distance of 1 960 km 1 220 mi 16 It sets the new tropo FM DX record for Europe At the same time FM DXers in Poland received FM radiostations from Moscow for the first time via troposphere at distances 1 100 kilometres 684 mi 1 300 kilometres 808 mi On November 2 2020 Maltese based Param DXer received FM stations from the Valencia region across the Mediterranean in early morning due to extreme tropo ducting The distance accounts for around 1 365 kilometres 848 miles It is exceptionally rare that such signals made their way to the island despite being out of the tropo season See also EditMW DX Skywave Radio propagation Tropospheric scatter Velocity of propagation Thermal fade Clear channel station Federal Standard 1037C Looming and similar refraction phenomenaReferences Edit DXing com The Web Resource for Radio Hobbyists Universal Radio Research November 2 2016 Retrieved November 12 2016 Rijn Muntjewerff s TV DX Netherlands 1961 2005 Todd Emslie s TV DX Page Todd Emslie Retrieved November 12 2016 WTFDA FM ALL TIME DISTANCE RECORDS AS OF 2 1 16 WTFDA org Worldwide TV FM DX Association February 1 2016 Retrieved November 12 2016 archived FERNANDO GARCIA North America s champion of tropo TV DX THE TV DX EXPOSITION Retrieved November 12 2016 JEFF KRUSZKA S RECORD BREAKING DTV TROPO as received in south Louisiana THE TV DX EXPOSITION Retrieved November 12 2016 Emel XPLORADIO 9 12 2004 gigantyczne tropo UHF i FM XPLORADIO Retrieved 2018 07 01 https youtube com cPsi0GPeiXc dead link TROPO MA to FL 97 9 WRMF Worldwide TV FM DX Association WTFDA Forums June 2007 Retrieved November 12 2016 archived My FM DX Records XPLORADIO Maciej Lugowski Retrieved 2018 07 01 EMEL DX 2011 09 19 FM DX 1700 KM TROPO archived from the original on 2021 12 20 retrieved 2017 10 10 Kjell SM7GVF ex SM4GVF Best DX worked by SM7GVF from JO77GA Retrieved November 12 2016 WA5IYX DTV DX Screen Captures Retrieved November 12 2016 Aug 24 25 2009 Es er Tropo Worldwide TV FM DX Association WTFDA Forums August 2009 Retrieved November 12 2016 archived https www fmlist org fm logmapt php datum 2016 09 28 amp band Tropo amp target ALL amp rxin ALL archived FM DX Tropo Log Tomaszow Mazowiecki Poland Archived at Ghostarchive and the Wayback Machine Tropo 98 5 DR P4 Holstebro Mejrup Denmark 1960 km YouTube DXing FAQ Worldwide TV FM DX Association Retrieved April 25 2005 William Hepburn s VHF UHF Tropospheric Ducting Forecast William Hepburn s TV amp Radio DX Information Centre Retrieved June 12 2006 Tropospheric Ducting YouTube Channel of FMDXUA 1 Bellevue NE DX Photos Matthew C Sittel s DX Page Archived from the original on September 27 2007 Retrieved April 26 2005 a href Template Cite web html title Template Cite web cite web a CS1 maint unfit URL link Jeff Kadet K1MOD s TV DX Photos Archived from the original on 2015 03 01 Retrieved 2015 03 02 oldtvguides com Retrieved from https en wikipedia org w index php title Tropospheric propagation amp oldid 1144341218 Tropospheric ducting, wikipedia, wiki, book, books, library,

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