[TowerTalk] Wide spaced Yagis

[Joe Reisert]

Richard,

Extra elements add wind load and cost to a Yagi antenna and in some case 
this an important consideration. Minimum number of elements is also all 
that is needed for narrow bandwidth (such as using only the 20 meter cw or 
ssb band but not the entire band).

However, if properly designed, a Yagi antenna with an extra element (or 2!) 
can provide additional bandwidth and perhaps raise the input impedance. 
Hence, can obtain better efficiency and easier matching. In some cases (see 
below) Yagis can be fed directly with a 50 Ohm transmission line! Not a bad 
compromise (at least on 20 meters and above where antennas are smaller!).

Furthermore, if an element is damaged, broken or the antenna has ice 
loading, the Yagis with greater number of elements than required will often 
still perform, albeit at a lower gain.

Some examples of the above are in my article "Yagi/Uda Antenna Design, Part 
1: A Different Approach" in Communications Quarterly, Winter 1998 edition, 
page 48.

I hope that this throws some light on the situation.

73,

Joe, W1JR


At 08:37 PM 7/31/01 -0700, 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?
>
>
>
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Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!!  http://www.anwireless.com

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