Re: [amsat-bb] Cheap Yagi Antennas for VHF/UHF: experiences?

["Frederick M. Spinner" <fspinner@xxxxxxxxxxx>]

>I have printed the Cheap Yagi article and have read it a few times. I have 
>a question I hope someone can help with. I know I must be missing something 
>obvious.
>The drive element shows L and H. what is the TOTAL length of the driven 
>element including the turn and return part of the element? Is the total  L 
>+ H + 1/2L.

Close... actually its L + H + 1/2L + spacing of J (1/2"=>1" depending on the 
band)  Cut the wire a little long, shape the J correctly, and trim off the 
extra off the other end.

>Also on the 144 Mhz how do I add additional directors? The first
>part of the article says "... the ability to grow with the same
>element spacing..." but the lengths in the tables have different
>lengths and spacing.

Send an e-mail to Kent Britian and ask him.  Unfortuately, it is simple if 
you are the guy who designed the originals, but if I remember correctly, he 
used YagiMax to design the rough antennas and then used the YagiMax'ed 
models in NEC to optimise.  I think K5OE said once that the J-matched 
elements designed to be fed, if they were normal straight elements, with 
like, 17 ohms impedance.  (3:1 impedance transform ratio with the "J" 
match).  But don't hold me to that.

So the simple answer is, unless you already are fairly good at modeling 
antennas, there isn't a simple answer.

>One last question:  If I use brass welding rods that are 36 inches
>long, and join 2 with a piece of brass tube, will the increase in
>diameter for this joint impact performance ?

I'm assuming your doing this at 2m?  It shouldn't be a problem at all IMHO.  
  You are looking at a potentially very small fraction of a wavelength (or 
fraction of the element length) that you'll have that tube sleeved in.


Good Luck

Fred W0FMS


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