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Re: Umbrella dish antenna

Hi Maggie.

maggie@voicenet.com writes:
> Oh, well-done, Howard! I'm working on a design for a small stressed 
>  parabolic dish inspired as a scaled-down version of the K2RIW design 
>  (ARRL Antenna Book, 18th edition, ch 19).

That really is a fine piece of work.  After meeting Howard in 
Houston/London/Guilford, I'm still undecided if he is a genius or just plain 
crazy :-)  Not only does he get an A for effort, you can actually talk to him 
on AO-40 on his projects!
>  I'm contemplating what's basically a variation on my mutant K5OE helix 
>  for the feedpoint (Drake mounted to PVC pipe, feeding through a 
>  reflector (likely will put a can around this one). Then a-ways down the 

Here is a picture of an easy-to-build and match helix feed, any length.  I 
make no claims for circularity, but it is easy to set up and get working 
without any measurement tools.  Leave the 1st 1/4 turn flat against the 
bottom of your cup.

This feed is designed for no PVC pipe core.  If you plan to use PVC pipe to 
wrap the feed around, then use the smaller dimensions corresponding to 1" PVC 
(about 1.375") on your original helix.  I have been unable to get a 1-1/4" 
PVC core (about 1.55" dia) to work properly as it severely de-tunes the 
helix.  The smaller-than-you-would-design diameter around the 1" PVC core 
seems to counteract the malevolent effect.

>  We'll see if I can make that go. I've been itching for a way to improve 
>  my S-band RX without actually spending money.    

... ahhh!  The search for the holy grail.
Jerry, K5OE  
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