Thanks to all for the information. Below are the replies received. They
supply just what I need to carry out further research. Many thanks!
73,
John K4IQ
>In brainstorming some new antennas, an issue arises. With a four square
>made up of 4 inverted L's, suspended from orthogonal catenaries off a tower,
>what effect, if any will the central supporting tower have upon the phasing
>and subsequent pattern of the four-square?
----
I'm using something similar to what you're trying to do here. 4-square
built around a 120' tower (two 2L 40, two 5L 10 on tower). The verticals
are 90' slanted verticals, each base 100' (not 1/8 wavelength!) from the
tower, top about 40' from the tower. The top of the verticals bisect a
45' piece of wire with rope on each side, one tied to the tower, the other
tied to trees about 150' or so into the woods. Sort of a slanted T shape
for each one.
Each has 4 raised radials, I probably should have more. Do not tie them
together. More info is in a document on the YCCC web site at
http://www.yccc.org - let me know if you can't find it, or if you want any
more info!
73 - Tom
--------------------------------------------------------------------
E-mail: frenaye@pcnet.com
Tom Frenaye, K1KI, P O Box 386, West Suffield CT 06093 Phone: 860-668-5444
----
I intend doing the same with a 90 feet tower - my
idea was to use T-sloping top verticals if
you understand what I mean!
Let me know what you get back. KF4HK from Comtek
send me a few layouts and on some
of them there is a tower in the middle but he
does not say if it is detrimental or not.
Tnx and HNY
Bernie
ZS4TX
---
Hi John....
as modeled in AO-6 and AO6pro...yes the tower will interact with the
Inverted L's.....it will lose a significant amout of the F/B that you
would expect from the 4 square.....how much interaction and loss of
gain will depend on the electrical height of the center tower......a
tower that is 130 feet tall with a couple of large yagi's on top will
be significantly taller than a 1/4 wave on 160......then there is a
lesser effect....at least I think so.....I would be interested in
hearing about other replies you get from some that maybe have built
an exact copy of what you are proposing....I run a somwhat similar
system on 160.....
140 foot main tower with 25 feet of rohn 45g rotary mast above the
main tower....165 feet total height....tower has a 4 high stack of 5
el HG205's 2/2 40 meter cushcrafts @ 160 / 80 feet....rotary
dipole for 80/75 at 145 feet....5/5 on 10 mtrs @150' / 116'
fixed 5/5 on Japan 15 mtrs @132' / 93' + 5L 15Mtr fixed on S.AM
@50'
the 160 meter antennas are 75% of full sized 1/2 wave dipoles 4 of
them.......mounted like inverted V's only vertically.....feed points
are 92 feet away from the tower....phase fed with a much modified
ComTek switchbox..........it works!
de John K9UWA
topband DXCC #60 255 / 253
topband WAZ #15 40 / 40
---
Subject: PS....re: Radials
Priority: normal
I think that elevated radials are a waste of time and they will cost
you too much of your needed height to install....on 160 they would
have to be at least 15 to 20 feet high to work correctly...besides
all the latest antenna guru's say that they still are not as good as
radials...lots of them on the ground......have you thought about how
you are going to feed these antennas???? An inverted L that is only
85-90 feet tall will have a feedpoint impedance of around 20-24 ohms
assuming perfect ground plane.....100 radials on each one....and no
even if they are on the ground...run a Buss Wire from tower out
between each antenna and where the raials from each antenna meet the
biuss wire terminate them to the buss...
de John K9UWA
----
If the tower structure is resonant on 160m, there will indeed be a large
effect on the Inv-Ls.
If you send me the info on the tower (height, HF beams and their height,
etc.), I'll be happy to model it (and therefore see the effect of the
tower on the 4-sq array) with the inv-L 4-square (I assume the inv-Ls
will be spaced 1/4-wave from each other, as is usual in a 4-square
array).
Since elevated radials MUST be tuned (to 1/4-wave resonance), it only
seems logical that they should be connected only where they come together
at the feedpoint location of each inv-L. Unless you insulate radials for
the different Inv-Ls from each other, you'll probably run into problems
tuning them to resonance.
73, de Earl, K6SE
----
From: Patrick Collins <pcollins@freenet.columbus.oh.us>
Subject: Re: TopBand: Four-square antennas/ interaction effects
To: John Mitchell <jbmitch>
Why don't you use the center element as a driven element and hang
parasitic elements from it?
---
If the tower is resonant on 160 and you are building a 160m array, it will
TOTALLY destroy the radiation pattern of the 4 -square. You wqill have to
detune the tower to shift its resonance away from 160m.
Elevated radials are very different from buied radials, they are (when you
use a small number) resonant devices, just like you would have a very low
dipole. Hence, you should NOT interconnect these radials where they fross.
Using 4 instaead of 2 radials makes no difference, just more wire.
73
John, ON4UN
----
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|