[TowerTalk] re:Force 12 Stack
Pete Smith
n4zr@contesting.com
Mon, 07 Feb 2000 10:59:26 -0500
At 09:30 AM 2/7/2000 -0800, Jay Terleski wrote:
>
>
>Ron,
>
>The C4 C3 stack will work fine. I am guessing you will use the single
>feed line models. You must compensate the Stack by not using identical
>feed line lengths but feed one with a small delay line length of coax to
>compensate the driven element (sleeves) difference in horizontal spacing
>when pointing in the same direction.
An excellent point, though the offset for the C-4 is a small one. The
C-4XL requires significantly more.
>
>
>The other thing I would suggest is that you shorten your proposed
>spacing to 27 ft.
Also agreed -- my modeling showed 28 feet, but that's within the margin of
error. you can find some details, and pattern plots, in my 8/9-95 NCJ
article titled A Preliminary Look at Improved Stack Spacing for Short-Boom
Tribanders.
>
>C3s are short booms and modeling has shown us that 27 feet is about the
>best and widest compromise for gain and pattern.
>
>Also model the stack to make sure your setting these antennas to obtain
>the pattern you want. At 100 feet and 75 feet you will have a very good
>DX signal but probably not so good a signal to US. You might consider a
>third C3 at 50 feet. Then you could also put the upper one in phase
>with the one at 50 feet and have a very wide spaced stack. This
>provides high angle lobes for E-skip and F skip close in work.
I have modeled something very close to this, and the results are
disappointing. Even though the middle antenna is undriven, it seems to
"participate" anyway, to the detriment of gain and F/B. A better solution
might be a 1X/2X/3X stack (antenna heights of 1/3, 2/3, and the full
tower), with provision for switching among them. Running all 3 antennas
together does a good job of concentrating power in the first lobe and
cancelling the second, and you could still drive the bottom one only, for
domestic purposes.
73, Pete N4ZR
Don't forget to update your entry in the World Contest Station Database
http://206.102.70.3/search.htm
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm