40m openings

K3NA at aol.com K3NA at aol.com
Fri Dec 9 22:36:13 EST 1994

Mike N0BSH commented on the JA opening on 40m during 1930-2030Z in the WW CW
weekend and asked how it might work.

I took a look at this opening, using the following assumptions:
-- transmitter at St Paul MN
-- A index = 5
-- SF = 78
-- Nov 26th

The path to Japan has a range of about 9300-9400km.  At 20z it parallels the
auroral oval, but does not enter it.  After examining a range of takeoff
angles from 0 to 5 degrees (the only ones which carry far enough at this
time) I decided to look at the 5 degree takeoff angle in more detail.

Basically, this opening is a continuation of the short path morning opening
on 40m. It is clearly not a long path opening (as Mike confirmed); the long
path at 20z runs its first 10000km or more in daylight and also crosses the
geomagnetic equator in the daylight sector.  Absorption levels in this
illuminated portion of the long path will soak up the signal long before it
reaches the more-friendly night sector.

As daylight illuminates the short path over Canada, the first hops convert to
E-layer refractions.  For example, at 18z this path to Japan is 2 E hops plus
as many as 4 F hops for a maximum range of 13-14,000 km (Philippines).

By 18:45z the absorption has increased such that the last F hop is no longer
achievable.  2E+3F still can reach 11-12,000 km, enough for Japan...

A half-hour later the steadily building ionization over Canada/Alaska
introduces another E-layer hop.  The 3E+3F (6 hops) is back to a range of
13-14,000 km.

At 19:30z increased absorption at the USA end eliminates another F-hop.
 However the 3E+2F path is just long enough to reach Tokyo with the 5 degree
takeoff angle.

Takeoff angles above 5 degrees will not propagate far enough to reach Japan
during the time mentioned by Mike.  A high antenna will be needed to get
enough energy into the ionosphere in the 4-5 degree range to take advantage
of this path geometry.

At 20:45z Alaskan ionization levels force a 4th E-layer hop.  The 4E+1F path
geometry has a range of only 8000 km and is not long enough to reach Japan.
 At this point 40m probably closes between JA and St Paul with the 5 degree
takeoff angle.

Lower takeoff angles such as 2 degrees may work for another hour or even
longer.  Eventually the path becomes all E-layer hops and signals at these
very low angles will be quite weak.  (Of course, getting a 40m beam up high
enough to have significant radiation at a 2degree take off angle will be
quite an achievement in itself.  And in Japan someone will also have to be
listening with a low-takeoff angle antenna as well.  From a practical
standpoint, it's not feasible to get enough transmitter power into these
angles to make a useful signal.)

   -- Eric K3NA

>From John W. Brosnahan" <broz at csn.org  Sat Dec 10 02:45:16 1994
From: John W. Brosnahan" <broz at csn.org (John W. Brosnahan)
Date: Fri, 9 Dec 1994 19:45:16 -0700
Subject: N0BSH's commentsabout the afternoon 40M path to the NW
Message-ID: <199412100245.AA02710 at teal.csn.org>

Mike, your comments about the NW path on 40M in late afternoon are interesting
in that I didn't know that the path went that far east.  (ie I was hoping
that we got it and nobody else did!)  If you look at the grayline in
Geoclock MAP9009 format you will see that the terminator for sunrise
is moving across that part of the world at that time.   So the entire
path is essentially a gray line path.  You are close enough to sunset
for the absorption to have dropped way down and signals can be quite
I worked a JT1 on that path a few days before CQWWCW just before 4:00 p.m. 
local and hoped he would show up for the test.  But no luck.  Talked to Ron, 
N0RR, who knows and loves 40M and he said that the path is one that he worked 
a lot from California back when he lived there, but that he hadn't seen that 
much of it from Colorado.
Still my favorite time on 40M was back in the 80s from K0RF's old place, when
his 40M 3L Yagi was still only at 100ft.  I worked a number of JAs and 
northern Europeans at high noon.  Just beam north and scatter.  Signals
are weak but can be copied, if you can get their attention.  Of course 
it is night time on that side of the world and there is lots of activity
and QRM so it is difficult to attract any pileup, but S&P can net
a couple dozen qsos during mid day.  You can't count on the path but it
is important to check 40M throughout the day if you really want to be
Enjoy it when you can, because it is not only very seasonal but there just 
isn't much activity to take advantage of it even when the path is there.
73  John  W0UN

>From Willy Umanets <uw9ar at chal.chel.su>  Sat Dec 10 15:13:19 1994
From: Willy Umanets <uw9ar at chal.chel.su> (Willy Umanets)
Date: Sat, 10 Dec 94 10:13:19 -0500
Subject: 40M propogation
Message-ID: <AAFMSwkSK2 at chal.chel.su>

Mike, nobody is going to be able to give you a good
explanation on 2000z direct path to SE Asia on 40m!
It is just one of those features of the "BLACK HOLE".
Take it as granted and enjoy it! Black hole is THE
place to go to for CQWWCW, now I know.
73, Willy, UA9BA
JV "Challenger Ltd"                 phone : 351-260-0190
Internet : uw9ar at chal.chel.su       fax   : 351-237-1756

More information about the CQ-Contest mailing list