> From: Michael Tope
> I think what everybody is trying to say is that for a fixed 40 ft
> boom length, you don't gain much by increasing the number of
> elements beyond 4. That doesn't mean that 5 can't or won't work
> as well as 4, it just means that 5 won't work much better than 4
> unless you lengthen the boom beyond 40 ft.
That depends on what you mean by "5 won't work much better than 4."
If you are talking forward gain, you're correct - gain is
proportional to boom length. If you're talking about maintaining
gain over more of the band, or SWR bandwidth, or maintaining F/R
over more of the band, then the five element design may be "better"
than a four element design on the same boom length.
For example, if one uses the YO 40 foot boom 5 element antenna as
a starting point, forward gain (free space) is 9.95 +/- .07 dB
across the entire band ... F/R is 24 +/- 1 dB across the entire
band and SWR is less than 1.5:1 across the band. If one element
is removed, gain drops by less than .2 dB (9.8 +/- .3 dB) ... F/R
drops to 18.5 +/- 5 dB and SWR bandwidth (1.5:1) becomes less
than 300 KHz.
Stretching the 5 element design to a 56 foot boom buys about 1 dB
of gain over the 40 foot 5 element design ... F/R and SWR bandwidth
remain about the same.
... Joe, K4IK
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