In a message dated 9/3/01 4:25:47 AM Pacific Daylight Time, 2@vc.net writes:
>
>In building a 1/2 wave dipole 4 SQR 40 meter array, the answer to this
>question was critical in my understanding of why the positive side of the
>dipole went up and why the distance between the tops of the dipoles (ends
of the positivie side) was critical in making the array a better performer.
>Bringing the tips of the dipoles out away from one another and positioning
>them over the feedpoints made the average spacing between elements improve
>the array. It also helped me understand why the bottom of the dipoles
>(negative side) could be positioned to better fit my tower installation
>without the distance between them being as critical. Understanding 1/2
wave dipole theory, as it pertained to where the antenna radiated most of
it's
>energy, was important. In practice, moving the tips of the top of the
>dipoles away from each other made the array better by improving the F/B
and
>making it more efficient, explained by the radiation pattern of the 1/2
>wave dipoles. I think it was/is a good topic for TT.
tnx, Paul.
It seem that, like Sears' auto batteries, hamdom's old
wives' tales Die Hard. cheers
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
>>
Good observations Paul and Rich. I think any aspect of this "So-Called
Dirty
Non Money Making Theoretical Aspects of Antennas Is Appropriate" for a
Reflector even though it's over the head of some.
There is another theoretical concept as dirty as it is that when you use
longer than 1/4 waves for a 4 square, you may not get as clean a pattern due
to the higher mutual coupling between them. I thought that 4 1/2 waves in a
4 Sq should give a better pattern. My preliminary Eznec tries were not
good.
K4VX told me that a freind of his put up 4-5/8's waves and then found in
actual practice and in soft ware the patterns go to hell. Now what it will
take to improve it I don't know and don't have time to play games with it
now. I had hopes of making 4 Sq with 1/4 waves and then for the "K7CCO
Magnum Contest Model" I'd add wire extensions to 1/2 or 5/8 wave with
dirigibles. Unless I can get more gain this project has been cancelled.
Another design concept is to use just one of a 4 Sq 1/4 DE's and use the
others as reflectors. The length of the feedlines shorted, or use a
variable
XL or Xc switched in can tune the reflectors. What the DE Z will be I don't
know yet but should be well below 50. So an L network at each 1/4 wave
vertical is a possibility. Or make them longer than a 1/4 wave and just add
a series Xc so that 50 ohms is obtained.
I'd like to use a Parasol top loading on 160M. It will be a long winter
night project. See Al Christman K3LC article in 10/00 QST p43 for this
design. It can be fed at the top where the top loading wires branch off and
down at about 45 degrees for loading and top guys. 1/8 wave high the Z's
are
above 20 ohms. Fed at the top of the 1/8 wave towers it's about 40 ohms as
I remember. If the vertical 1/8 wave part is made 10' longer on 160M, 50
ohms is obtained there. Additional length would be needed to compensate for
the Z lowering of the 3 reflectors. Since 1/4 waves start at around 36 ohms
and go down with loading and parasitic elements, lengthening the 1/4 wave is
an easy way to get higher Rr's that few use. This gets to be a very
reasonable size on 80&40M. I'll try it on 40M first. Has anyone tried this
yet even with full size 1/4 waves using 3 reflectors? It sounds so good
maybe I'll try it in Eznec right now. I have some data on this now but not
enough to share. Theoretical discussions like this are how new ideas are
developed. I'd like to see far more of it. This is the year 2001 and we
need some "fresh designs" without the usual TT nit picking by those who have
never tried it and instead of "constant rehashes." Lets start a friendly
contest of who can come up with the best "new ideas." k7gco
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|