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

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Subject: [TowerTalk] Improving the 402-CD (was Weatherproofing for copper coils?)
From: (Steve Miller)
Date: Sat, 1 Sep 2001 10:29:45 -0400 (EDT)
N3RR wrote:

> Why re-invent the wheel?  

Because I want a better wheel.

> This is a 20 year old, PROVEN, antenna.  

So was the 105-BA, 155-BA etc. now we have the 105-CA ....

> Plenty of articles tell you how to solve the problems you guys are 
> asking about now.  Why not just follow them?

I have not seen articles on weatherproofing the type of coil I intend 
to use.  Any references would be welcome.

> Go to Leeson's book and several QST articles, do what they tell you to do,
> and be done with it.  

This was done years ago but does nothing to improve gain and pattern.

> The inductance is well-known.  Shrink wrap that costs
> $2/foot is a BARGIN.  So it will cost you $16 in shrink-wrap.  It will solve
> your problem easier than winding coils of unknown inductance and resuls.
> What am I missing here?

I plan to use large 4'5" diameter coils similar to those shown in W6KW's 80 
meter Yagi article (July 1998 CQ).  My thought was to shrink wrap the tubing 
rather than the entire coil (requiring 80 feet of shrink wrap for two 
antennas) and was hoping for a solution that costs less than $160.  I've 
received one suggestion to use plasti-dip, but need to check on its loss 

> Yes, I have two of these antennas up at 67/134 ft (stack).  Yes, I beefed
> them both up to QHS++ and added RR++ as well.  Yes, I used additional shrink
> wrap on the coils.  Yes, they work magnificantly.

CC 402-CDs work fairly well, but they can be improved.  The form material 
and geometry of the loading coils suggest the Q can be greatly increased.  
Q estimates between 150 and 330 have been reported although I have not 
measured the Q directly.

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,


For K1KW, the 402-CD coils are the most lossy part of the antenna.  
Replacing them with higher-Q versions will give you more gain and 
slightly sharpen the SWR curve.  I need a better handle on the actual 
Q of the CC coils before tossing out numbers from the models....

Steve Miller   N8SM

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