[600MRG] 630m Opportunity Time Windows Based on Wedge Overlaps on UTC Circle

[James Hollander]

All, please share your comments and suggestions about this opportunity time windows thread.

73,  Jim H    W5EST
 
OPPORTUNITY TIME WINDOWS BASED ON WEDGE OVERLAPS ON UTC CIRCLE

    In general, the 630m opportunity time window(s) for reception of a 630m station by a second station are comprised of each UTC time interval they share darkness.  Each window begins with the latest sunset SS (Z) of the two stations that puts both of them in darkness, followed by the earliest sunrise SR(Z) of either of the two stations that brings it into sunlight.
 
   Of course, SS and SR are only signposts and not hard boundaries on the 630m operating road. Some of this discussion may need correction when our ongoing experience on 630m demands it.  Numerous locations in the world have no 630m amateur or experimental stations yet.  The watchword in "opportunity time window" is "opportunity" because some skywave signals, especially from closer stations, can be received before SS and after SR. And other signals can appear and fade out one or more times some hours after SS or before SR.  We are likely to find that 630m is particularly rich in rule-exceptions and interesting signal propagation instances and non-instances that are not yet well understood.

      This opportunity time window concept can also be more restrictively defined (subject to exceptions) by the interval between SS at the westward station and the SR at the eastward station.  One time window formula of this type defines the window length as:
 
    Window Width W = [SR(of eastward stn Z) -0.5hr] - [SS(of westward stn Z) + 1.0 hr].
 
For one instance of an exception, however, a high-latitude station in one hemisphere can have its opportunity time window defined by both the SS and SR at one same low-latitude station at a near longitude whether in the same or opposite hemisphere.
 
     Outside the scope of this discussion of opportunity time windows are random signal variations, solar/ geomagnetic variations, ionospheric weather, and some seasonal variation in the minimum D-layer absorption level in the time window. The SS/SR definition of the window operates as if 630m reception were subject only to D-layer signal absorption, which may be a good start but not the whole story.

VISUALIZING OPPORTUNITY TIME WINDOWS WORLDWIDE WITH TIME WEDGES

    To visualize opportunity time windows generally, draw a 24 hour UTC circle.  Pie chart wedges or arcs on the circle represent night-time durations for each 630m station.  Position the radius (bisecting line) in the middle of each respective pie chart wedge to point to the corresponding astronomical midnight UTC (Z) at the station location regardless of the northern or southern hemisphere location of that station.  The longitude difference (not exceeding 180 degrees) of the station locations corresponds to the angle between those midnights on the UTC circle.

   One can instead use four different-colored poster push-pins--say, black SS1 and yellow SR1 for one station and blue SS2 and orange SR2 for the other station--as SS/SR pairs on the UTC circle.  Each SS/SR pair defines the darkness hours for its 630m station.  

    Visualize the night-time wedges at first as dark half-circles at an equinox.  Each wedge contracts from length 12 hours after a hemisphere's spring equinox to a minimum at its summer solstice and then returns to length 12 hours at its fall equinox.  Each wedge expands from length 12 hours after a hemisphere's fall equinox to a maximum  at its winter solstice.  Each wedge overlaps more or less with the other wedge, or does not overlap at all.

    The wedge overlap of darknesses represents the opportunity time window(s) for 630m reception.  If the station locations are in opposite N. and S. hemispheres, one wedge expands as the other wedge contracts.  Otherwise, in the same hemisphere, they both expand or contract in tandem.  If the wedges represent stations at different latitudes, the higher-latitude wedge expands and contracts at a faster rate and reaches a more extreme maximum or minimum arc angle at solstices than the lower-latitude wedge does.  References to "migration" mean that the time position (Z) in the middle of the opportunity time window varies over weeks of time.

     The wedges can be variably shaded to indicate a roughly one-hour ascent of signal to noise ratios SNR into night and a half hour descent of SNR into morning.  (The ascent and descent vary randomly and may be shorter or even much longer in duration.)  The most favorable portion of the window for both stations can be around the time (Z) near the end of local night at a particular station before the descent of SNR begins there, but may occur earlier in the opportunity time window.  That particular station is the station that has the earliest sunrise SR (Z) of either of the two stations that brings it into sunlight. 

    I've found this wedge approach most helpful for picturing 630m time windows worldwide.  One also can use a gray line map such as at DXatlas together with the wedge approach.  Perhaps more experience with 630m DX will lead to improvements.  

   For a future post:  Qualitative conclusions and predictions worldwide implied by the wedge approach for 630m.   


WEBSITES
http://www.dxatlas.com/   Gray-line map, polar/azimuthal projectionson your center.
http://www.gcmap.com/  Great circle mapper
SR/SSsites:
    http://www.sunrise-and-sunset.com/en
    http://www.timebie.com/sun/
Worldtime:
   http://www.worldtimezone.com/
--end--