Hi Dave,
Thank you for your very detailed and insightful reply. Based on what you
have written and my understanding of my situation I will stay with the 1/4
wavelength radials for now.
Tnx & 73
Bob KQ2M
-----Original Message-----
From: Artek Manuals
Sent: Wednesday, November 18, 2020 9:01 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 4 square question Part III and NEW questions Part
IV
Bob
I have two vertical antennas ( actually a T and an L) for 160 and 80
with 4 separate elevated radials each .
I did a lot of VNA testing early on looking for interaction. As long as
the radials crossed at an angle and did not run parallel to each other
there was no measurable interaction. . Connecting the radials at
crossover points created problems some of that may have been due common
mode currents which I was not focused on at the time.
The above was done with 1/4 wave radials. Later I switched to
non-resonant radials. The good news is the models suggested slight
improvement in efficiency . There is a very good article in
Communications Quarterly, spring 1997, by Dick Weber K5IU , on the care
and feeding of elevated radials. "Optimal Elevated Radial Vertical
Antennas". Which inspired much of what I have done in my current setup.
I have tried contacting Dick on a couple of questions last year but my
email either went into the SPAM folder or he isn't answering emails
these days For my particular ground type I found that 80-90' radials.
seemed to produce the desired effect which had more to do with impedance
matching systems.
A couple of things about non resonant elevated systems is that impedance
matching can become quite a complex problem . Think of an elevated
radial vertical as an odd shaped off center fed antenna and you begin to
understand the problem. Also Common mode currents can be quite large and
require robust CM chokes
More later if you need
Dave
NR1DX
On 11/17/2020 8:50 PM, kq2m@kq2m.com wrote:
Hi,
I want to thank K0PJ/9, W9PL, AC0C, W6RMK, W7VJ and VE9AA for your
willingness to help and all the valuable information and insight!
Sorry for the delay in my response but I have been working day and night
professionally and in clearing woods, building antennas, etc. The limited
daylight now is another large factor. ;-)
I have some new questions and would appreciate your insight and help:
1) In the past I have used 1/4 wavelength ELEVATED radials for my 80 meter
wire 4-square but AC0C mentioned that it would be beneficial to use
radials that were NOT 1/4 wavelength. Should the radials be longer?
Shorter? By how much? I assume that all the ELEVATED radials be the same
length regardless of what fraction of wavelength is used – is that
correct?
2) An old 4-square has 1/4 wavelength wire elements that have grown into
the trees. There is no way to get them down but I can cut a small length
off of them so that they are non-resonant and not attached to anything.
Will that be okay or is there going to be a problem with them causing
interaction if these elements are within 1/2 wavelength of the new wire
4-square with ELEVATED radials?
3) The only place the feedpoint of my 160 Inv L can go on my property is
about 120’ - 130’ from the nearest feedpoints of the wire elements of my
80 meter 4-square and probably somewhat closer to the elevated radials.
Is this going to cause a significant interaction problem? I can ensure
that the elevated radials of the 160 Inv L do not cross those of the
elevated radials of the 80 Inv L if that would help. Would that help?
4) The SW element of the 80 meter 4square will be within 5’-10’ feet of
the guy wires of my 130’ tower from four ropes will support the elements
of the wire 4-square. The guy wires are broken up into non-resonant
lengths with insulators as follows starting from the tower 4’, 4’, 4’, 16’,
16’, 28’, 28’, 28’. The NW and NE elements will be about 15’ away from
the guy wires.
Will this be enough to prevent interaction with the tower guys or will the
4-square radiation pattern be adversely impacted?
Thanks in advance for your insights and help!
73
Bob KQ2M
-----Original Message-----
From: Jeff Blaine
Sent: Saturday, October 31, 2020 4:51 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 4 square question Part III
Bob,
My 2 cents here. There is a practical answer and an ideal answer to the
"which direction do my radials point."
My answer is that you space them so that they are not overlapping and
share the maximum separation with respect to the feed & with each
other. I also choked on both ends of the feed my verts to try to
contain the elements and the radials as the only intentional radiators.
Opinions vary as to this need but I'm personally a big believer in
conductive elements participating in the antenna thing unless you do
something to prevent that in advance.
On the other hand, unless you specifically measure the actual radials
and use a length somewhat off of 1/4 wl exactly, then the result is
almost certainly that one of the radials will hog the current and that
will bend your pattern on that one vertical.
So one answer is that it does not matter, and the other answer is that
it matters a lot if you want to peel the onion back another layer and go
for a more optimized installation. The problem with that is the benefit
of doing it in a more complicated way is probably lost on most guys
anyway because the improvements are not determinable in advance. A 4SQ
is a magical beast that will work "good enough" even with terrible
compromises and construction - where an optimized one is not really
appreciated because most hams don't have a way of doing a before/after
sort of evaluation.
Good luck!
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|