[SADXA] Explanation / Discussion -- 40m F-Layer DX Propagation Corridor MAP

[W7EXG (Bill)]

TO: SADXA MEMBERS
FROM: Bill Davis W7EXG
12/16/16

Larry Brown sent out a PDF file of the Angular Range for the 40m Propagation
Corridor I had previously presented.  At the recent SADXA meeting, it was
suggest that some written guidance regarding the use of this 40m DX aid
would be of value.  

Here is some guidance in understanding and using the 40m DX Aid recently
provided. 

BEARING MAP AND TERMINATOR VARIATION

A.	The BEARING MAP, was generated by NS6T, and is centered on Tucson. 
B.	The Yellow Lines represent the SUNSET and SUNRISE Terminator. 
C.	This Terminator varies about NORTH (360 deg) from 23.45 degrees to
-23.45 degrees as shown. 
D.	ON DEC 21st 
	a.	The SUNRISE Terminator is shown from 23 deg to 203 degrees
	b.	The SUNSET Terminator is shown from 337 deg to 157 deg. 
E.	ON JUNE 21st 
	a.	The SUNRISE Terminator is shown from 337 deg to 157 degrees
	b.	The SUNSET Terminator is shown from 23 deg to 203 deg. 
F.	ON MARCH 21st and SEPT; 21st, The SUNRISE AND SUNSET Yellow
Terminators are from 360 degrees to 180 degrees. (NOT SHOWN)
G.	The EQUATION for Angular Variation of the Terminator relative to
North pole is:
                Terminator Angle (TA) = 23.45 SIN [(360/365)(N-81)]
               Where N = # of the DAY in the current YEAR. 
	    For Example, March 21st is DAY 81, so TA = 0 degrees.  

TUCSON 40m DX BEARING AT TIME OF TERMINATOR

A.	The Maximum 40m DX Angular Range AT TIME OF TERMINATOR is about +/-
38 degrees.  
B.	AT SUNSET - [OR SUNRISE] - You have the opportunity to work 40m DX
stations with bearings up to +/- 38 degrees ABOUT THE TERMINATOR ANGLES.
C.	The MAP with +/- 38 degree arrows indicates possible areas or ranges
of the world where 40m DX might be possible from TUCSON on dates below. 
For Example:  
	On Dec. 21st SUNRISE - the +/- 38 Degree Arrows show the 40m DX
range AT SUNRISE, with a 23 degree Terminator. 
	On Dec. 21st SUNSET - the +/- 38 Degree Arrows show the 40m DX range
AT SUNSET, with a 337 degree Terminator. 

The bearings of the potential DX entities within the +/- 38 Degree range
about the above Terminators is also shown.  

WHY +/- 38 Degrees?

The +/- 38 degrees was derived from the fact that the DAY EMUF < 7 MHz at
about a 2600 mile Propagation DAY Corridor from the Terminator. This assumes
trans-equatorial propagation. This also insures 40m F layer DX propagation
in this Corridor.   If a bearing Azimuth angle is > +/-38 degrees, then the
40m DX Signals will exceed the 2600 mi DAY Corridor relative to the
Terminator, and signal will enter into a poor E layer propagation region. 

TUCSON 40m DX TIME WINDOW RELATIVE TO TERMINATOR

The information above is based on TUCSON being AT THE TERMINATOR. 

In reality, there is a 40m DX Propagation TIME WINDOW of +/- 2.6 Hrs about
the Terminator. 

However, the angular propagation bearings must change, to be compatible with
your DX station and F-Layer DX Propagation Corridor. 

For Example:
	A. When station is 2.6 Hrs from SUNSET - Station Antenna bearing
MUST be TOWARDS the TERMINAOR (Towards Night), and NOT AWAY FROM the
TERMINATOR (Into DAY). The Maximum Angle relative to the terminator --- is
76 degrees ONLY towards NIGHT to insure no more than 2600 mi propagation
into the DARK side of the Terminator, or 2600 mi into the DAY side of
Terminator -- anywhere in the world. This insures F-Layer 40m DX.  

	B. When station is 2.6 Hrs from SUNRISE - Staion Antenna bearing
MUST be TOWARDS the TERMINAOR (Towards DAY), and NOT AWAY FROM the
TERMINATOR (Into NIGHT). The Maximum Angle relative to the terminator --- is
76 degrees ONLY towards DAY to insure no more than 2600 mi propagation into
the DAY side of the Terminator, or 2600 mi into the NIGHT side of Terminator
-- anywhere in the world. This insures F-Layer 40m DX.  

WHY 2.6 HOURS BEFORE AND AFTER TERMINATOR?

	AFTER SUNRISE -- The 2600 mi DAY Propagation Corridor has EMUF < 7
MHz, and takes a station about 2.6 Hours to travel. Thus for 2.6 Hrs, the
F-Layer DX is accessible for 2600 mi from the Sunrise Terminator. 

	BEFORE SUNRISE - The 2600 mi NIGHT Propagation Corridor has EMUF < 7
MHz, and takes a station about 2.6 Hours to travel to Sunrise Terminator.
However, 2.6 Hrs prior to Sunrise, the 40m DX signal will travel in DARK
until the Antipode, and then will travel Long Path out into a possible
2600mi DAY DX station. This station would still be in the 40m DAY F-Layer DX
Propagation Corridor, due to the 76 degree restriction.  

FINAL NOTES

NOTE1: These guidelines are to take advantage of the DAY time F-Layer DX
Propagation Corridor. You can always point your antenna > +/- 38 degrees
about the terminator, or > 76 degree guidelines per above discussion.  This
just means your going to kill the DAY F-Layer 40m DX Propagation Corridor. 

NOTE2: Most Hams do NOT have a 40m Directional Beam (other than
dipole/inverted V orientation). 40m Dipoles favoring 23/203 degrees, or
337/157 degrees or both may have best overall 40m DX value for Terminator
Enhanced 40m DX propagation at SS and SR times. 

NOTE3:  If you have a fixed 40m Antenna, listen 2.6 Hrs BEFORE AND AFTER
Sunrise and/or Sunset for best Terminator Enhanced 40m F-Layer DX.  This
will be your BEST 40m DX opportunity in which F-Layer 40m DX is enhanced
around the world during the DAY. It is possible to plan your 40m DX
operations, for a specific DX station. It is entirely possible, the LONG
PATH 40m DX may occur, 2 Hrs before your SUNRISE, with the path going
through the Antipode, into the DAY region on opposite world, for a DX
station 2 Hrs AFTER their Sunrise. This is similar to the 40m Heard Island
Propagation. 

NOTE4: As we move into the Low Solar Cycle, the minimum MUF will decrease
BELOW 7 MHz at night. Thus 40m will be DEAD at night. However, at about
Sunrise, MUF > 7.3 MHz, and 40m F-Layer DX will become active. It will
remain active until about 4 Hours AFTER SUNRISE, [or 4 Hours BEFORE SUNSET],
when EMUF < 7.3 MHz.   These two 4 Hour Time Windows will most likely be
YOUR ONLY 40m F-Layer DX Windows during LOW SOLAR. Notice LOW SOLAR actually
provides BETTER DAYTIME F Layer DX opportunities (+/- 4 Hrs vs +/- 2.6 Hrs).


FINAL NOTE: I think that most of us are well aware that best DX is often
before, during, or after the terminator timeframe. Here we are not
discussing TOPBAND, but rather the 40m band.  40m is unique in that it has a
40m 2.5 hr., 2600 mi. DAY F-Layer DX Propagation Corridor relative to the
Terminator. This was ONE of my key points in my presentation. 

I Hope this explanation has value to all. Please feel free to ask questions
regarding any or all of this material. Hopefully, most of your SS and SR 40m
experiences annually, will demonstrate most of these principles. 

Best 73s, and good 40m DX. 

Bill W7EXG
W7EXG at Q.COM