Richard Karlquist wrote:
> I noticed in Chapter 8 of W2PV's Yagi book, he shows that for a 20 meter
> Yagi on a 54 foot boom, there is little difference in gain whether you use
> 4, 5, or 6 elements. What I don't understand is why you never hear of a 54
> ft 4 ele Yagi, but 5's and even 6's are commonplace. This is kind of
> analogous to the question of why people bother with 4 element Yagi's on a 30
> ft boom when a 3 element on that boom has slightly more gain. I notice in
> the ARRL antenna book, there are a bunch of reference designs for Yagis.
> The 10 meter ones are more widespaced (in wavelengths) than the 20 meter
> ones. Why? Seems like they should be scale models of each other. Am I
> missing something here?
Well, I don't think you are missing anything really mysterious here. 54 foot
booms are hard to make strong enough to stay up through years of rough
weather. It has been done but it wasn't easy (or cheap). You could probably
make a boom 40 feet long for half the cost and with half the weight in
aluminum. On ten meters, a boom equivalent to a 54 footer on 20 meters is only
27 feet long . . . easy and cheap.
Also, I don't think the information in W2PV's book is really widespread
knowledge among average hams, even those who have monoband Yagis, so it should
not be too surprising that is not applied often.
I think the most import point, however, is "bragging rights". It is common to
hear someone brag about the number of elements they have but rarely do you hear
them bragging about their boom length. Most hams simply "feel better" about
owning a 6 element 20 meter beam than they would about owning a 4 element 20
meter beam regardless of the relative performance of the two. This is just
"human nature" and has nothing to do with real antenna performance. K6ASL once
had a 5 element 20 meter Yagi on a 60 foot boom . . . very impressive. It was
up about a year until an irate neighbor cut the guy wires . . .
Stan
w7ni@easystreet.com
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