[SADXA] 40m Daytime US DX Propagation Corridor - from Bill W7EXG

Tue Nov 20 21:58:18 EST 2018

Hi Dave,

I noticed via QRZ that we were both born in same year and lived in Oregon (I
in Eugene) when you received W7AQK in 1955 and I received W7EXG in 1956. We
also graduated from the U of A in 1966, although my degree was Electrical
Engineering. So in some sense, we have some commonality. 

My career at Motorola was way to busy to spend much time thinking about
propagation. After retirement and after much Engineering consulting, I
finally had time to think about his subject.

I recall as a kid wondering about whatever happened to the A, B and C
layers?  Little did I know, the Heavyside Layer (Named after its predictor)
was later called the E layer, since it was initially defined as the Electric
Layer. As more layers were discovered, D Layer followed below the E, and F
layers followed above the E.  

Although there are many variables that affect propagation, there are some
basics that are fundamental as a starting point of study. Initially focusing
on these propagation fundamentals, might convince you to postpone your
bowling objectives. 

I am suggesting that 40m DX is prevalent during most of the day in the US,
during these upcoming winter months, centered on Dec. 19th. This is the day
that the northern solar terminator is closes to the US. 

A study of the E layer behaviors after Sunrise relative to the sun's solar
terminator show that 7 MHz signals will propagate through this E layer to
the F layer for stations as far as 2800 miles from the terminator. This is
because a 7 MHz signal is less than EMUF in this daytime region and will not
be reflected by the E layer. 

So a good starting point for understanding this discussion is to understand
the E layer and EMUF as it relates to propagation. What happens if operating
frequency f < EMUF, or f > EMUF.  Most 160m operators are well aware of the
impact of EMUF on 160m propagation during LOW and HIGH solar periods. 

I have been known to state that the E-Layer plays as much a dominant role in
DX propagation as the F-layer. The E layer is an enabler or an inhibitor for
F-layer DX. It is the GRID of the Fleming Valve. Yes the Cathode and Plate
are important, but it is the GRID that controls what is happening. 

Also, a visualization of how the EMUF increases orthogonally from the
terminator, will help to visualize the 40m DX corridor 2800 miles wide and
parallel to the Terminator throughout the world during the day. 

You are correct that polar-regions can receive such intense ionization along
the magnetic field lines during a solar event, that the D layer ionization
is significantly enhanced to absorb all signal energy. 

However, as pointed out above, the archive 40m DX maps for DEC 19th DURING
THE DAY, show plenty of 40m daytime propagation from the Mid West / Eastern
US to Europe. I agree that Western US has a bit more challenge due to the N
Polar Aurora region. 

However, you are correct to understand I am not suggesting this is the best
time or best band to work Europe. In fact, I believe most people might
suggest this is the absolute WORST TIME!!  Hi Hi. 

All I am really suggesting is the entire US has a 40m DX opportunity during
the day (except maybe during solar noon)-- for the next few months. The 40m
signal paths must at least stay within the 40m propagation corridor during
the day. This does not preclude the daytime signal path from also entering
into a nighttime propagation path. This behavior is evident in the 40m
daytime DX maps.  

Hope this helps Dave, and thanks for your comments. 

Best 73's
Bill W7EXG

-----Original Message-----
From: sadxa-bounces at mailman.qth.net [mailto:sadxa-bounces at mailman.qth.net]
On Behalf Of w7aqk
Sent: Monday, November 19, 2018 7:33 AM
To: 'Southern AZ DX Association E-Mail Reflector'
Subject: Re: [SADXA] 40m Daytime US DX Propagation Corridor - from Bill
W7EXG

Bill and all,

I read your postings with considerable interest.  I've never really been 
much of a student of propagation, except for the most rudimentary forms of 
prognostication.  To be honest, it's always a bit difficult for me to 
confirm or deny various predictions because my antennas are relatively 
simplistic.  There might be a good opening, but I'd still be apt to miss 
it!!!

I'm not sure I fully understood everything you posted, but I think I got the

gist of it.  Admittedly, at first I thought you were going to conclude that 
I should possibly take up bowling, but apparently you anticipate some 
"better" conditions in the offing.  Which brings me to my question!

You are suggesting (I think) that towards mid December there may be some 
improvement in 40 meter propagation.  In the recent past, on another 
reflector, I commented on my difficulty working into the U.K. from here, 
although I was somewhat more successful working into southern Europe.   A 
friend on that reflector introduced me to the concept of the "auroral oval",

and suggested that this was a large part of my problem.  Apparently this 
hangs over the northern part of the globe, gets larger and more problematic 
in winter, and tends to block propagation from here to those northern 
European latitudes.  In essence, it suggest that it might be easier to work 
northern Europe outside of the window you are suggesting.  Is that true, or 
am I misinterpreting things, mixing apples and oranges, etc.?

Cheers!

Dave W7AQK

-----Original Message----- 
From: W7EXG (Bill)
Sent: Sunday, November 18, 2018 6:35 PM
To: 'Southern AZ DX Association E-Mail Reflector'
Subject: Re: [SADXA] 40m Daytime US DX Propagation Corridor - from Bill 
W7EXG

FOOTNOTE: The northern terminator curvature referenced below is the apparent
terminator curvature on a Mercator world map projection, when the solar
terminator is also projected.

In reality the terminator is a linear circular boundary around the world,
but appears curved when mapped as noted above.

Bill W7EXG

-----Original Message-----
From: sadxa-bounces at mailman.qth.net [mailto:sadxa-bounces at mailman.qth.net]
On Behalf Of W7EXG (Bill)
Sent: Saturday, November 17, 2018 9:55 PM
To: 'Southern AZ DX Association E-Mail Reflector'
Subject: [SADXA] 40m Daytime US DX Propagation Corridor - from Bill W7EXG

11-17-18
TO: SADXA MEMBERS
SUBJECT: 40m Daytime US DX Propagation Corridor

On Dec. 18th, the northern solar terminator boundary is only about 1089
miles from the US northern border during solar noon.  This northern
terminator is also about 2200 miles from Tucson during solar noon.

During my past propagation presentations, I pointed out that the E-layer
Critical frequency (foE), and resulting EMUF (Max Usable Frequency for the
E-Layer) does NOT exceed 7 MHz for about 2800 Mi from and orthogonal to the
Sunrise terminator. This data (from Ionograms (foE vs Time)) is easily
obtainable from the 120+ vertical RF sounding digital Ionogram sites located
throughout the world at various latitudes.

Since on Dec. 18th, MOST of the US is less than 2500 Mi from the northern
terminator during solar noon, most any RF signal on 40m in the US with an
elevation angle of about 23 degrees (most 40m antennas) will NOT be
reflected by the E layer, and will ONLY be reflected by the F-Layer (DX
region -- 23 deg 745 mi / hop), provided the MUF of the F layer is greater
than 7 MHz.

This described behavior is even more pronounced during LOW SOLAR periods,
since the ionization of the E layer is diminished, even at solar noon,
extending the < 7 MHz EMUF boundary further below the US southern boundary.

NOTE:  This distance [orthogonal from Terminator to EMUF = 7 MHz boundary]
is latitude dependent, and decreases from northern latitude values to a
minimum value at the Equator [by about 10%].

In practice, there are two additional 40m effects that occur in the US:
1) At solar noon, the D layer can still be heavily ionized, absorbing
RF energy across this boundary.
2) The Western region BEFORE solar noon, and the Eastern region AFTER
solar noon experience the northern terminator curvature descending
southwards towards the US, further decreasing the EMUF values, decreasing
D-layer absorption and thus further enhancing the daytime F-Layer DX
propagation.

Please observe the DXmaps propagation archives for this date and timeframe
which clearly demonstrates this described daytime US 40m DX behavior.

Note that during the summer, this described effect does not occur, since the
solar  noon terminator is North of the North Pole, and the E layer is fully
ionized, with an EMUF > 7 MHz. This results in E layer propagation (23 deg -
250 mi / hop) throughout most of the day in the US on 40m during the summer.

Also, during HIGH SOLAR periods with the E layer significantly more ionized,
only the northern most portion of the US may experience this daytime DX
propagation effect during December. This is due to the reduced orthogonal
distance from the terminator to EMUF < 7 MHz boundary.

BOTTOM LINE:
40m DX in the US during the day is BEST during the winter months centered on
Dec. 18th, and BEST during LOW SOLAR.  We are currently approaching this
BEST/BEST scenario.

As a matter of interest, please post your 40m DX exploit's during this
upcoming winter season, especially very late morning and very early
afternoon 40m DX QSOs.

73's, and Happy DXing.

Bill W7EXG

______________________________________________________________
SADXA Website http://www.sadxa.org

SADXA mailing list
Home: http://mailman.qth.net/mailman/listinfo/sadxa
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:SADXA at mailman.qth.net

This list hosted by: http://www.qsl.net
You can support qsl.net: http://www.qsl.net/donate.html

______________________________________________________________
SADXA Website http://www.sadxa.org

SADXA mailing list
Home: http://mailman.qth.net/mailman/listinfo/sadxa
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:SADXA at mailman.qth.net

This list hosted by: http://www.qsl.net
You can support qsl.net: http://www.qsl.net/donate.html 

______________________________________________________________
SADXA Website http://www.sadxa.org

SADXA mailing list
Home: http://mailman.qth.net/mailman/listinfo/sadxa
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:SADXA at mailman.qth.net

This list hosted by: http://www.qsl.net
You can support qsl.net: http://www.qsl.net/donate.html