On Sat, 1 Sep 2001 10:29:45 -0400 (EDT) Steve Miller
<millersg@dmapub.dma.org> writes:
> > Why re-invent the wheel?
>
> Because I want a better wheel.
>
> I plan to use large 4'5" diameter coils (sic)
I don't think the elements will support 4 FOOT 5 INCH
diameter coils ! N4KG :-)
> CC 402-CDs work fairly well, but they can be improved.
How far below a FULL SIZE 2L Yagi is a 402CD
in gain? Maybe 1 dB?
How much improvement can you expect from
a shortened (loaded) Yagi, even with Lossless coils?
My guess is you might get close to 1 dB more gain
but you will still have limited bandwidth due to loading.
Have you considered plating the coils?
Note that F/B and GAIN typically do NOT peak with
the same tuning / spacing of the elements. To achieve
peak F/B, gain is usually reduced by around 1 dB.
The exceptions to this rule of thumb are for 3L Yagi's
on a 0.25 WL boom or 4,5,6L Yagi's on a 0.75 WL boom
where gain and F/B tend to peak at the same frequency.
If F/B is a major concern, the best solutions are to either
stack a pair of 2L Yagi's or go to a 3L Yagi, optimized
for F/B (typically 7.0 - 7.5 dBi free space gain) on a
35 ft boom for 40M. Going to a 48 ft boom (0.35 WL)
will yield another dB of gain at somewhat less F/B.
Tom N4KG
> My design started with the CC-402 and used AO to optimize a better
> design
> (not just better coils) that fits within the 402-CD turning radius.
> Using
> high Q coils, it has about 1 dB more gain and 5 dB better
> front-to-rear
> on CW compared to the original CC-402CD assuming 402-CD coil Q of
> around 200. A slightly lesser improvement is seen on SSB.
>
> Hope this helps,
>
> Steve
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