You are correct, Ward. That info is only part of the whole story.
Clearly as can be seen in my previous chart, the vertical has a lower
takeoff angle, but it is not clear how the gains compare at some very
low angle. So here is a new table comparing both antennas (3 element 20
meter Yagi) and looking at the gains at only 5 degrees elevation. All of
this data is over average ground.
Height _ Horz Antenna _ Vert Antenna ___ Difference
20 ______ 2.6 dBi ________ 0.3 dBi _____ 2.3 dB (vertical wins)
30 _______ 0.7 dBi ________ 2.0 dBi _____ 1.3 dB (vertical wins)
40 ______ 3.1 dBi ________ 2.8 dBi _____ 0.3 dB (horizontal wins)
50 ______ 4.9 dBi ________ 3.7 dBi _____ 1.2 dB (horizontal wins)
80 ______ 8.6 dBi ________ 6.2 dBi _____ 2.4 dB (horizontal wins)
100 _____ 10.2 dBi _______ 7.6 dBi _____ 2.6 dB (horizontal wins)
120 _____ 11.3 dBi _______ 8.7 dBi _____ 2.6 dB (horizontal wins)
150 _____ 12.5 dBi _______ 9.9 dBi _____ 2.6 dB (horizontal wins)
200 _____ 13.2 dBi _______ 10.8 dBi ____ 2.4 dB (horizontal wins)
300 _____ 10.2 dBi* _____ 8.8 dBi* ____ 1.4 dB (horizontal wins)
* 5 degree elevation angle is past the first lobe peak.
As to which height is best for DXing, I think you will get a bunch of
different answers, because it depends on probability of angle of DX
signal arrival which is different for everyone (but may have a general
bound). The best height for general purpose use (both USA and DX) is a
little easier question. My best guess for that one would be 80 feet
over flat ground for 20 meters.
Jerry, K4SAV
Ward Silver wrote:
>K4SAV generated some useful numbers  thank you.
>
>    
>Here are some EZNEC numbers for a three element Yagi
>turned either vertically of horizontally.
>
>Height ___ Horz Antenna ______ Vert Antenna ____ Gain Difference
>20 ______ 9.6 dBi at 36 deg ___ 4.8 at 17 deg ______ 4.8 dB
>30_______11 dBi at 28 deg _____ 5.7 dBi at 15 deg __ 5.3 dB
>35 _____ 11.6 dBi at 25 deg ____5.9 dBi at 13 deg __ 5.7 dB
>40 _____ 11.9 dBi at 23 deg ___ 6 dBi at 12 deg ____ 5.9 dB
>80 _____ 12.7 dBi at 12 deg ___ 8 dBi at 9 deg _____ 4.7 dB
>100 ____ 12.9 dBi at 10 deg ___ 8.8 dBi at 8 deg ___ 4.1 dB
>120 ____ 12.9 dBi at 8 deg ____ 9.4 at 7 deg _______ 3.5 dB
>150 ____ 13 dBi at 7 deg ______ 10.1 dBi at 6 deg __ 2.9 dB
>200 ____ 13.2 dBi at 5 deg ____ 10.8 dBi at 5 deg __ 2.4 dB
>300 ____ 13.1 dBi at 3 deg ____ 11.6 dBi at 3 deg __ 1.5 dB
>    
>
>This is only part of the story, however. Look at the angle for peak gain
>for heights of 80 feet or less. Which is more useful for DXing? It is also
>useful to compare the difference in gain between the two antennas as a
>function of vertical angle. You will find a dramatic difference in favor of
>the vertical antenna at low angles, which are precisely the takeoff angles
>needed for opening and closing bands and for minimizing the number of hops
>over really long distances, such as from the Pacific to Europe. Mounting
>the yagi vertically is not a panacea, but in some circumstances makes a big
>difference.
>
>73, Ward N0AX
>
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