[antennaware] 105CA modeling

[leewells@lexmark.com]

Thanks for the help with the tapered elements in NEC.  I didn't realize
the taper correction included shortening the elements.

After plugging in the new numbers from Roger, the models look just as expected.

I tried two things with the 105CA model.

First I tried moving the 1st director on the 105CA about 3" closer to the driven element.
I may need to do this when I side mount the antenna (side mounting on a self supporting
tower with a wide face - 28") to have enough clearance.  Moving the element didn't have
too much of an effect.  If I shorten the 1st director by 0.125" on either side, then
the gain curve is almost identical.  The impedance shifts a little, but I'm not sure
what the SWR will look like after the beta match.  The real impedance shifts up by about
2 to 2.5 ohms from 28.0 - 28.6.  Hopefully this won't make too much of a difference.


Next was to try NW3Z's OWA techniques to see if I could get a good 50ohm match
and better bandwidth (gain & swr) by adding one more element.  Natan already has
a design for a 10m 6-el on a 24 ft boom.  The problem I had is that I'm trying to
side mount this antenna, and one of the elements in his design is just 11" off of
the mounting point.  So I tried leaving the 105CA elements in place, adding
one element about 8-10" from the driven element, and then re-tweaking the element
lengths to see what I could get.

Here's about the best I could do:  (gain in dBi freespace   SWR is 50ohm)

28.0	10.02 dBi	1.65:1
28.2	10.20		1.45:1
28.4	10.32		1.37:1
28.6	10.34		1.37:1
28.8	10.23		1.40:1
29.0	 9.95		1.78:1

The gain isn't quite as high as the original 105ca (but close).  The SWR bandwidth is 
a little better, and is direct 50 ohm feed.  But is it worth an extra element just
to get a 50-ohm match???  Probably not.  I think I'll just leave well enough alone.

I couldn't get anywhere near the curves that Natan got with his 6-el beam.  He gets better
that 10dBi from 28.0 - 29.2 (but the peak gain isn't as high as the stock 105ca), and 
50 ohm SWR is better than 2:1 from 28.0 - 29.2.  Having the 2nd director out a 
little ways seems to make the difference.


	--Lee - KT4ZX
	

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