K6HI wrote:
>I clicked on LB's quad url you gave, but did not see the comparison with the
>45' 3el Yagi. What was the difference?
See http://www.cebik.com/quad5.html (It is 5 elements...not 3)
About half way down the page see "5-Element 20 Meter Quads and Yagi
- Free Space Gain". The 5 el Quad on a 40' boom peaks at about 10.4 dBi
and the 5 el Yagi on a 45' boom peaks at about 10.3 dBi. However the
Yagi has a much flatter gain curve from 14.0 to 14.3 (10.1 at 14.0 to
10.3 at 14.2 to 10.2 at 14.35). The Quad goes from 8.0 at 14.0 to 10.4
at 14.3 to 10.4 at 14.35. From the text, W4RNL notes that the Quad is
apparently optimized for gain only with very poor F/B and SWR bandwidth
compared to the Yagi which is well optimized for all three.
Now look at http://www.cebik.com/q3l.html
About 3/4 down the page see "3-Element 20 Meter Yagi vs. Quad -
Free-Space Gain" for 24' boom antennas. Here you'll see the Quad has about
a 1.7 dBi gain advantage. I believe this agrees with the previous comments
that, for smaller antennas, a Quad has higher gain than a Yagi for the same
boom length. However, as boom length increases, the difference narrows
substantially. For example, K2OB's boom 5 element 80' boom Quad peaks just
under 12.0 dBi and N6BV's YO-optimized 6 element 80' boom Yagi peaks at 12.1
dBi. With all fairness, the latter is a computer-optimized design and I
doubt that the Quad is since tools like YO are not as readily available for
Quads.
Bottom line to me is Quads beat Yagis for short booms and Quads
equal Yagis for long booms. Given no major electrical reasons favoring
Quads, Yagis tend to win out in popularity for long-boom antennas because
of their relative mechanical simplicity and low maintenance. BTW Yuri's
60' Razor for 15 meters is 1.28 wavelengths and is equivalent to a 90' boom
on 20 meters, so it is definitely a LONG boom!
73, Bill W4ZV
P.S. Last post from me on this topic...the W4RNL site has several other
pages of interest on quads for those interested.
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