On 4/14/15 5:44 AM, Peter Voelpel wrote:> Why is a difference of a 1/16"
of element length a disaster with an antenna
> to cover 430-438MHz?
>
a long boom Yagi with many elements has fairly critical lengths to get
the side and back lobes down. Forward gain isn't strongly affected, though.
10 MHz BW is 1%.
1/16" (actually 0.125" total element length) out of a 12" element is also 1%
If you're looking for -20dB or -30dB side/backlobes then 1% kinds of
errors can be a problem.
These kinds of designs are optimized for one frequency (432, usually)
and while they might show decent feedpoint match for a fairly wide
frequency, their pattern probably isn't very good 5MHz away from the
design frequency.
Element length in long boom yagis is like surface smoothness in a dish.
Huge dings in a dish don't change the gain much, but boy, do they
create sidelobes.
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