So you are lengthening the boom length to 20 feet. I thought the
discussion was comparing a Tennadyne T8 to a 3 element Steppir. Does
the Tennadyne T8 use a parasitic director for 10 meters? Sure, if we
just allows things to get "just a little bit longer" we can start to
get better performance from the LPDA. But the 3 element SteppIR is
sitting on a 16 foot boom. I wouldn't argue a T10 or T12 is closer
to the performance of the 3 element SteppIR, but that wasn't what was
originally stated.
-Scott, WU2X
On Sat, Jan 23, 2010 at 3:26 PM, Steve, W3AHL <w3ahl@att.net> wrote:
> Your model of the 8-element LPDA was apparently done from a formula and
> wasn't optimized at all. Although I do agree that 6 & 8 element logs are
> sub-optimum. But an optimized design for a 9 element 14-30 Mhz LPDA on a
> 20' boom will average closer to 6.5 dBi with 17 dB F/B, except at 20m, where
> it drops to 5.7 dBi & 11.3 F/B in free space. Add a 10m director and you can
> get 7+ gain with 30 dB F/B on 10M (with a 4' boom extension).
>
> And stacking an LPDA does have unique issues. Anything that disturbs the
> current phasing in the active-element region will distort the pattern more
> than with a standard yagi design.
>
> Steve, W3AHL
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