[TowerTalk] Quagi Optimization

[Jim Lux]

At 07:13 AM 2/20/2006, Pat Barthelow wrote:
>Sorry for the slightly off topic query, and please guide me to the best
>antenna discussion group....I am at a remote location, (Sierra Foothills
>above Auburn CA,) and built Wayne Oberbecks Late 70's version, 16 el Quagi
>for 440 to try to hit the hometown repeater, ( Monterey CA) some 160 miles
>away, driven with 5 watts.  I can hear the repeater sometimes,  but cant
>quite key it.
>I want to know what the most sensitive dimensions are that affect gain.  My
>aluminum welding rod/wood boom/copper quad loop quagi, probably has some
>dimesnional inaccuracies of up to 1/2 ", probably the driven loop size or
>flatness, and some of the director element spacing  vary from the Oberbeck
>model, vary in spacing while lengths conform pretty tight.  They may also
>vary in perpendicularity to the boom  (some slightly bent, or not 90 deg  to
>the flat boom, so their tips may be out of whack, say by 1/2  to 3/4
>inch.... With only rough tools, what dimensions do I have to pay attention
>to most, to get the best gain out of this antenna?  How about  the not
>having a balun problem?
>73, DX, de Pat AA6EG aa6eg at hotmail.coim

Can you send me the dimensions (or point me to an online source of them, or 
if they're in the ARRL antenna book).  I can run a model pretty quickly and 
tell you what's the most sensitive.

In general, elements closer to the driven element are more critical (they 
have more current). Length is more critical than orientation, since the 
length sets the phase of the current in the element (1% change in length 
results in a couple degree change in phase). Spacing is also fairly 
important (1/2" is about 6 degrees of phase) Small changes in orientation 
aren't all that big a deal: the coupling is, to a first order, proportional 
to the cosine of the angle,and the difference between cosine(0) and 
cosine(5 degrees) is pretty small)

Jim