Topband: coupling

[Carl K9LA]

W4ZV asked me to post the D4 (Cape Verde) coupling loss data from my Low 
Band Monitor article.

Azimuth loss

0 2.2dB
10/350 2.3
20/340 2.4
30/330 2.8
40/320 3.3
50/310 4.1
60/300 5.2
70/290 7.0
80/280 8.2
90/270 9.6
100/260 8.9
110/250 7.0
120/240 5.7
130/230 4.8
140/220 4.2
150/210 3.5
160/200 3.2
170190 3.0
180 3.0

This is the coupling loss for only one entry into the ionosphere. 
Multiple hops would incur more loss based on the conditions at each 
entry/exit point. As can be seen, maximum loss is at 270 degrees and 90 
degrees from D4.

The only target areas to the west (250-290 degrees) are the Caribbean, 
Central America, and northern South America. But this is mostly over 
water and only 7000km or so, so perhaps it's not enough to worry about.

On the other hand, there are several target areas to the east (70-110 
degrees) at much greater distances: 9M2 at 14000km, YB at 15000km, 9V at 
14000km, etc. These would be the ones to worry about. If I was at D4 
doing a competitive contest, I'd seriously consider some kind of 
horizontal antenna to stack the odds in my favor for picking up these 
mults on 160m.

W8JI asked about potential error in the estimates of dB coupling. The 
coupling loss values come out of the math in magneto-ionic theory, and I 
would assume that any source of error would be due to the short-term 
variation of the ionosphere.

A while ago I received an e-mail from a G who told me about his 
experiences with this whole issue at equatorial latitudes on broadcast 
frequencies. But darned if I remember who this G was. Nor can I find his 
e-mail at the moment. But it was very informative, and indeed confirmed 
that verticals at these low latitudes were inferior to horizontal 
antennas when going east and west.

Carl K9LA