[Lowfer] Loops 101

[Bill Ashlock]

Peter,

>Would you say then that the optimum loop shape is a circle? Next in >line 
>is any form for which the range values of the "radius," ie,  the >locus of 
>points from center to perimeter, is closely equal, true? So >then, the 
>order of priority would favor: 1) a circle, 2) large
>equal-sided polygons, 3) a square, 4) a rectangle of unequal sides,
>finally, a triangle?

According to the most thorough text book coverage I can find the AREA is the 
controlling parameter for radiation efficiency Vs size. This means the 
circle is the best radiator for a given length of wire. However, given the 
50ft tall by 50ft diam cylinder, that many of us believe is the controlling 
size of the loop, the 50ft square loop has more area than the 50ft diam 
circle by 27% or 2.7db from a signal standpoint. However the circle has 27% 
less perimeter than the square and this amounts to a reduction in Rac (AC 
resistance) of about 20% when ground losses are factored in. This would be 
about +1db. The total advantage of the square over the circle would then be 
only 1.7db.

The order of priority for shapes 1 through 4 would, therefore, depend on the 
limits for height and width. Given the 'promised land' of no constrains the 
optimum loop shape would be in the order 1,2,3. The relative efficiency for 
the unequal sided rectangle (4) and triangle depend on the height/length 
ratios. But we're not talking major differences between any of these shapes. 
The best approach is usually to accommodate what your lot has to offer. The 
underlying theme should be (as you are gazing upward from your back yard) - 
It's area that counts. If you have some tall oak trees out there, get a line 
over them!

Bill



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