[600MRG] Opportunity Time Windows Based on Wedge Overlaps--Predictions Worldwide

[James Hollander]

This conclusions / worldwide predictions section is the concluding part of the Sept. 19 post on opportunity time windows. 

The paired examples of countries or regions are hardly exhaustive and omit many countries that may have stations coming on to 630m operations in the years ahead as well.  

Comments and suggestions on any parts of this conclusions / worldwide predictions section are most welcome.    
 
73,   Jim H   W5EST
 
UNEQUAL LATITUDES IN THE SAME HEMISPHERE
    Station locations at unequal latitudes in the same hemisphere have a variable-duration opportunity time window that expands and contracts with the seasons and that migrates somewhat on the 24 hour UTC circle. The time migration can depend on both the longitude difference and latitude difference between station locations.  The latitude/longitude differences can either augment or diminish each other's effects on time migration, details available on request.  In duration or length, the opportunity time window reaches a maximum length at the winter solstice and a minimum at summer solstice in that hemisphere.  Given a large enough longitude difference, the opportunity window may be closed (width = 0 hours) before fall equinox and correspondingly after spring equinox.  The date range when the opportunity window is open in the rest of the year decreases with greater longitude difference between station locations.   The central and southern USA compared to UK/northern Europe exemplify unequal latitudes in the northern hemisphere.  Likewise UK/EU compared to India.  Other examples are Alaska-Hawaii, and Alaska and the "lower 48."   In the southern hemisphere, examples could be any place like Sydney, Melbourne, and Perth in southern Australia paired with any of Cairns or Darwin or other parts of northern Australia.
 
SAME LATITUDE IN THE SAME HEMISPHERE
     Station locations at the same latitude in the same hemisphere have an opportunity time window that expands and contracts with the season, with a fixed middle-position on the 24 hour UTC circle.  Given a large enough longitude difference, the opportunity window may close (width = 0) as already described.  At the equator, the night-time wedges for both stations are exact semicircular 12-hour long wedges every day of the year.  Their overlap (opportunity time window) diminishes with the difference in station longitudes in a manner similar to the time window for stations having the same latitude generally.  Japan shares about the same latitude in the northern hemisphere with the middle-USA and southern Europe.  Alaska and Norway likewise share about their own same latitude.
 
SAME LONGITUDE IN THE SAME HEMISPHERE OR SAME LONGITUDE IN OPPOSITE HEMISPHERES
     Station locations at the same longitude in the same hemisphere or same longitude in opposite hemispheres have an opportunity time window that expands and contracts with the length of local night at the station with shorter local night. The window has a fixed middle-position on the 24 hour UTC circle, so no window migration occurs.  If either station has a sufficiently high latitude, the window may close for dates in a range centered on summer solstice at the lower-latitude station.  The width of that closed-window date range increases with latitude of the higher latitude station to a maximum at either the North Pole or South Pole.  Examples of places at similar longitudes are Japan and Australia, Alaska and Hawaii, eastern Canada and Venezuela, or central Europe and South Africa.
 
EQUAL BUT OPPOSITE LATITUDES IN BOTH N. / S. HEMISPHERES
    Station locations at equal latitudes in opposite hemispheres have a constant-width opportunity time window that migrates on the UTC circle with the season.  The amount of migration increases with the latitude difference and longitude difference between the station locations.  The central USA paired with southern Australia or northern New Zealand provide examples of these station positions.  Northern India or southern India respectively paired with southern Australia and northern Australia are further examples.  Reception is most likely best in a range of weeks centered near each equinox, especially if the difference in station longitudes corresponds to many time zones.
 
UNEQUAL LATITUDES IN OPPOSITE N. / S. HEMISPHERES
      Station locations at unequal latitudes in opposite hemispheres have a variable-width opportunity time window that migrates on the UTC circle and reaches a maximum at that solstice at which the station location with the larger latitude is in winter.  The time migration can depend on both the longitude difference and latitude difference between the station locations.  Details available on request.  Example of unequal latitudes in opposite hemispheres include Scandinavia and Australia, or Alaska and Australia, or northern/southern india paired respectively with northern/southern Australia.
 
TWO OPPORTUNITY WINDOWS IN THE SAME NIGHT IN ONE N. / S. HEMISPHERE AT OPPOSITE LONGITUDES
      Two opportunity time windows occur at the evening and pre-dawn hours of the same night for a first station at a moderate-to-high latitude in one N. or S. hemisphere and a second station located at the same or different latitude in a band of longitudes centered on the opposite longitude in the same S. or N. hemisphere.  One station's evening or morning reception in its local night would capture the other station's morning or evening transmission bounding the local daylight hours at that other station.  This type of double-window event probably can happen each year in a range of plus/minus about 7 weeks centered around the hemisphere's winter solstice.  Examples of such geographic locations include central and eastern Europe paired with Alaska and Hawaii, or Colorado/Saskatchewan paired respectively with south/north India.  In the southern hemisphere, eastern Australia would pair with eastern Brazil.
 
POSSIBILITY OF TWO OPPORTUNITY WINDOWS IN THE SAME NIGHT BETWEEN OPPOSITE HEMISPHERES AT OPPOSITE LONGITUDES
       In concept, two opportunity time windows could occur at beginning and end of the same night for a first station at a high latitude in one N. or S. hemisphere and a second station located at low latitude at essentially-opposite longitude in the opposite S. or N. hemisphere.  This type of event might happen at any of four times of year centered in weeks around time points about August 1, November 10, February 1 and May 10 (dates at plus/minus 7 weeks of winter and summer solstice).  It remains to be seen whether the windows would be wide enough for adequately decodable SNR of any presently-available digital mode.  An example of such geographic locations might pair Iceland with, say, Cairns in northern Queensland, Australia.  
 
ANTIPODES
      Station locations at antipodes regardless of the antipodes location have a zero opportunity time window. (Antipodes have equal but opposite latitudes and equal but opposite longitudes.)  Because of the delay after SS for SNR to ascend, and the interval before SR before SNR begins to descend, the 630m opportunity time window may be closed almost the entire year throughout a region extending for several hundred miles in every direction away from a given antipode.  France or Spain with New Zealand, or eastern Canada/USA-New England paired with the area around Perth in southwestern Australia provide some examples of near-antipodes.   Antipodal paths afford one more example where 630m operators can take up the challenge to go beyond the conceptual guideposts of the "opportunity time window" concept.
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