[TowerTalk] Improving the 402-CD (was Weatherproofing for copper coils?)

n4kg@juno.com n4kg@juno.com
Sat, 1 Sep 2001 10:07:10 -0600

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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