[SADXA] 40m Daytime DX Propagation Corridor

[W7EXG (Bill)]

TO: SADXA Members
FROM Bill W7EXG

For those who have been active recently on 40m during the day, you are
probably aware of the Daytime 40m DX potential. 

On Dec. 20-24, the northern boundary of the solar terminator is only about
1090 miles from the US border at Solar Noon. 

Since the EMUF is typically < 7 MHz for about 2500-3000 miles from the Solar
terminator at solar noon, the actual EMUF = 7 MHz boundary line is near the
southern border of the US, during US solar noon. 

Thus most of the US has a 40m DX region bounded between the Solar Terminator
and the EMUF = 7 MHz boundary line. Within this region, all f = 7 MHz
signals, have a conditions that f > EMUF. As a result, most 7 MHz signals in
the US will pass through the E layer and utilize the F DX layer during the
day. 

This allows for 40m F layer DX for Day-Day, Day-Night, and Night-Day
propagation. 

What makes this all a bit more exciting is for this DEC 2018, we are ALSO in
the LOW SOLAR Cycle period. Thus there will be even less ionization in
general, resulting in less signal absorption by the E and D layers, and
extending the EMUF boundary a bit further south. 

I hope the SADXA members will take a listen during the day for this 40m DX
opportunity in the coming weeks. Best times are within 3-4 hours after SR
and 3-4 hours before SS. 

40m DX at Solar Noon is a challenge, but there is a chance DX stations in
the northerly direction over the polar region might be heard and worked. I
have some interesting examples of US 40m DX, even at solar noon, over the
northern polar region. 

I am planning to present the nuts and bolts of this 40m Daytime DX
Opportunity at the Jan. 17th SADXA meeting entitled: Daytime 40m DX
Propagation Corridor

The important role of EMUF on 40m DX will be stressed, for enabling the use
of the F Layer. I will include some recent EMUF data (from foE ionogram
data) using world class ionogram sites at 4 different latitudes. From this
data, the 40m world wide Daytime DX corridor will be created and defined.
Some interesting examples of 40m Daytime DX propagation will be shown. This
data was gathered during this most recent December time period -- from the
40m DX Maps. This 40m daytime propagation data clearly exemplifies this
subject matter.

Since the members of this group seem to like a challenge, I was
contemplating a SOLAR NOON (+/- 1 Hr) 40m DX AWARD at the Jan. 17th
meeting!!  Our Solar Noon is currently about 12:20pm MST.  (Any Mode)
Good Luck!!  
 
Best 73's
Bill W7EXG