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Difference between revisions of "DXing Above 30 Mhz"

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Talk to most people about how far a VHF signal (above 30 Mhz) will travel, and most times, the answer will be 'line of sight'. However, as there sometimes is in nature, there's exceptions to the rule. Many phenomenon can cause a VHF and UHF signal to travel hundreds of miles or more. Events such as a stalled weather front to a meteor shower or even the solar wind can change things in the atmosphere and make a signal travel much further than normal.
 
Talk to most people about how far a VHF signal (above 30 Mhz) will travel, and most times, the answer will be 'line of sight'. However, as there sometimes is in nature, there's exceptions to the rule. Many phenomenon can cause a VHF and UHF signal to travel hundreds of miles or more. Events such as a stalled weather front to a meteor shower or even the solar wind can change things in the atmosphere and make a signal travel much further than normal.
  
The most common type of tropospheric ducting to impact scanner hobbyists and amateur radio operators results from a low-level temperature inversion. A low-level temperature inversion is a phenomena in which the temperature in the lower portion of the atmosphere, near the earth's surface, is considerably cooler than a layer further up in the atmosphere. This causes signals to be refracted thus resulting in a tunneling or ducting of the signals. Low-level temperature inversions can occur any time of the year but are often most dramatic (producing the most significant tropospheric ducting events) during the summer months. They are most often associated with surface high pressure which results in light near-surface winds allowing for radiative cooling affect. These events also commonly coincide with fog.  
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The most common type of tropospheric ducting to impact scanner hobbyists and amateur radio operators results from a low-level temperature inversion. A low-level temperature inversion is a phenomenon in which the temperature in the lower portion of the atmosphere, near the earth's surface, is considerably cooler than a layer farther up in the atmosphere. This causes signals to be refracted thus resulting in a tunneling or ducting of the signals. Low-level temperature inversions can occur any time of the year but are often most dramatic (producing the most significant tropospheric ducting events) during the summer months. They are most often associated with surface high pressure which results in light near-surface winds allowing for radiative cooling affect. These events also commonly coincide with fog.  
  
 
VHF, UHF and even 800 MHz and higher can be impacted quite significantly by these ducting events. One good example of very high frequencies being impacted is the anomalous propagation that plague the Doppler weather radar (WSR-88D) during the most extreme tropospheric ducting episodes.  
 
VHF, UHF and even 800 MHz and higher can be impacted quite significantly by these ducting events. One good example of very high frequencies being impacted is the anomalous propagation that plague the Doppler weather radar (WSR-88D) during the most extreme tropospheric ducting episodes.  
  
Hams (and folks involved in TV/FM DXing) have been studying this for years. Many of these phenomenon have been cataloged, but not are all well understood. If you are interested in a description of how a VHF signal (or above) can travel, take a look at this [http://en.wikipedia.org/wiki/TV/FM_DX article] on the WikiPedia site. Keep in mind that FM and TV broadcast, as well as ham frequencies, are found above 30 mhz. Techniques used in TV, FM and 2/432 Mhz DXing are applicable to DXing in the scanner bands.
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Hams (and folks involved in TV/FM DXing) have been studying this for years. Many of these phenomenon have been cataloged, but not are all well understood. If you are interested in a description of how a VHF signal (or above) can travel, take a look at this [http://en.wikipedia.org/wiki/TV/FM_DX article] on the WikiPedia site. Keep in mind that FM and TV broadcasts, as well as ham frequencies, are found above 30 mhz. Techniques used in TV, FM and 2/432 Mhz DXing are applicable to DXing in the scanner bands.
  
The links below are not intended to be comprehensive, but rather be a starting point for getting more information. Additional links with descriptions and maps are always welcome.
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The links below are not intended to be exhaustive, but rather be a starting point for getting more information. Additional links with descriptions and maps are always welcome.
  
The RR forum for discussing VHF/UHF skip can be found [http://www.radioreference.com/forums/forumdisplay.php?f=96 here]
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The RR forum for discussing VHF/UHF skip can be found [http://forums.radioreference.com/skip-tropospheric-ducting-forum here]
  
==Maps==  
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==Maps==
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* [https://www.dxmaps.com/spots/map.php DXMaps]
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* [https://www.fmscan.org/index.php?r=m FMScan.org]
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* [http://www.spacew.com/www/realtime.php Near Real Time MUF maps]
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* [https://www.radio-locator.com/cgi-bin/finder?page=Y Radio Station Finder]
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* [http://tropo.f5len.org Tropospheric Propagation Forecast]
 +
* [http://aprs.mennolink.org/ VHF Propagation Map]
 
* [http://www.dxinfocentre.com/tropo.html William Hepburn's Worldwide Tropospheric Ducting Forecasts]
 
* [http://www.dxinfocentre.com/tropo.html William Hepburn's Worldwide Tropospheric Ducting Forecasts]
* [http://www.vhfdx.info/spots/map.php?Lan=E&Frec=50&Map=NA&mycall=&myloc=&freq=&prop= V-UHF QSO Real Time Maps]
 
* [http://www.mountainlake.k12.mn.us/ham/aprs/ VHF Propagation Maps]
 
* [http://www.radio-locator.com/cgi-bin/finder?page=Y Radio Station Finder]
 
* [http://www.fmscan.org/index.php?r=m FMScan.org]
 
  
 
==Technical Articles==  
 
==Technical Articles==  
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* [http://www.gooddx.net/ The DX Robot] Automatic real-time AURORA and E-skip warnings via email or mobile phone
 
* [http://www.gooddx.net/ The DX Robot] Automatic real-time AURORA and E-skip warnings via email or mobile phone
 
* [http://www.kg0vl.com/ KG0VL VHF Aurora Radio Research]
 
* [http://www.kg0vl.com/ KG0VL VHF Aurora Radio Research]
* [http://home.swbell.net/pjdyer/index.html WA5IYX VHF Propagation Info]
 
  
 
==Other Propagation Links==
 
==Other Propagation Links==
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* [http://www.amfmdx.net/propagation/Es.html Mid-Latitude Sporadic-E (Es) - A Review]
 
* [http://www.amfmdx.net/propagation/Es.html Mid-Latitude Sporadic-E (Es) - A Review]
 
* [http://www.sv2agw.com/ham/vista_dxrobot.htm DX Robot VHF Propagation] Sidebar utility for Vista
 
* [http://www.sv2agw.com/ham/vista_dxrobot.htm DX Robot VHF Propagation] Sidebar utility for Vista
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* [[SNOTEL]] - indicator of VHF Low Band Skip
  
 
==TV/FM DX Links==
 
==TV/FM DX Links==
 
* Also see our [[MW DXing and Broadcasting]] article for additional related links
 
* Also see our [[MW DXing and Broadcasting]] article for additional related links
* [http://www.fcc.gov/mb/audio/fmq.html FCC FM Radio Database Query]
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* [https://www.fcc.gov/media/radio/fm-query#block-menu-block-4 FCC FM Query Broadcast Station Search]
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* [https://www.fcc.gov/media/television/tv-query FCC TV Query Broadcast Station Search]
 
* [http://www.fmtunerinfo.com/ FM Tuner Information Center]
 
* [http://www.fmtunerinfo.com/ FM Tuner Information Center]
 
* [http://www.dxfm.com/ FM/TV DXing from Lexington Ky.]
 
* [http://www.dxfm.com/ FM/TV DXing from Lexington Ky.]
* [http://www.odxa.on.ca/ Ontario DX Association]
 
 
* [http://www.radio.hobby.ru/ Russian Radio TV DX (in Russian)]
 
* [http://www.radio.hobby.ru/ Russian Radio TV DX (in Russian)]
 
* [http://www.skywaves.info/ Skywaves (UK)]  
 
* [http://www.skywaves.info/ Skywaves (UK)]  

Revision as of 08:24, 18 June 2019

Talk to most people about how far a VHF signal (above 30 Mhz) will travel, and most times, the answer will be 'line of sight'. However, as there sometimes is in nature, there's exceptions to the rule. Many phenomenon can cause a VHF and UHF signal to travel hundreds of miles or more. Events such as a stalled weather front to a meteor shower or even the solar wind can change things in the atmosphere and make a signal travel much further than normal.

The most common type of tropospheric ducting to impact scanner hobbyists and amateur radio operators results from a low-level temperature inversion. A low-level temperature inversion is a phenomenon in which the temperature in the lower portion of the atmosphere, near the earth's surface, is considerably cooler than a layer farther up in the atmosphere. This causes signals to be refracted thus resulting in a tunneling or ducting of the signals. Low-level temperature inversions can occur any time of the year but are often most dramatic (producing the most significant tropospheric ducting events) during the summer months. They are most often associated with surface high pressure which results in light near-surface winds allowing for radiative cooling affect. These events also commonly coincide with fog.

VHF, UHF and even 800 MHz and higher can be impacted quite significantly by these ducting events. One good example of very high frequencies being impacted is the anomalous propagation that plague the Doppler weather radar (WSR-88D) during the most extreme tropospheric ducting episodes.

Hams (and folks involved in TV/FM DXing) have been studying this for years. Many of these phenomenon have been cataloged, but not are all well understood. If you are interested in a description of how a VHF signal (or above) can travel, take a look at this article on the WikiPedia site. Keep in mind that FM and TV broadcasts, as well as ham frequencies, are found above 30 mhz. Techniques used in TV, FM and 2/432 Mhz DXing are applicable to DXing in the scanner bands.

The links below are not intended to be exhaustive, but rather be a starting point for getting more information. Additional links with descriptions and maps are always welcome.

The RR forum for discussing VHF/UHF skip can be found here

Maps

Technical Articles

Other Propagation Links

TV/FM DX Links

Worldwide TV FM DX Association (WTFDA)

Mailing Lists