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!
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 10/31/20 3:31 PM, jimlux wrote:
On 10/31/20 12:11 PM, kq2m@kq2m.com wrote:
I want to thank KK9A, NA6O, W4EF, SM2EKM, DCharing (callsign?) and
W6RMK, for all of their guidance, comments and links to helpful
sites. Greatly appreciated as always!
Now for the final question... let’s say that the “positions” of the
Gauge 12 or 14 THHN wire 4-square elements are N, E, S, and W,
arranged in a box with the sides broadside to NE, SE, SW, and NW and
all the elements will all have either 3 or 4 elevated radials. I
will be using the Comtek ACB4 (80) phasing box fed with each element
fed with 1/4 wavelengths of RG11 foam coax. (It’s the same phasing
box I have been using for the past 25 years).
Does it matter what directions the radials are pointing for each
element?
Not really - what the radial(s) do is provide a return path for the
current that "intercepts" the ground - and reduce "ground loss"
(independent of the "counterpoise" function).
The elements themselves are assumed omni directional. And it's only
some some sort of extreme cases (1 radial) that there's a more than
trivial effect on the directionality of the radiation pattern of a
single element. What changes is the efficiency (i.e. the loss
resistance gets lower as the number of radials increases).
In the usual 4SQ "current forcing" array with 3/4 wavelength feed
lines, the current in the element (which is what radiates) is the
right ampliude and phase to form the beam.
So let’s say I am using the NE position on the ACB-4 controller, since
I am radiating on all 4 elements, does it matter what directions the
radials are pointing? Do I want to have the same radial directions
with all 4 elements or do I want to spread out the radial directions
differently on each element? Since NE is by far the most important
direction for me (Europe), do I want to have more radials pointing NE
or broadside NE or equally spread out so that the radiation and
current return is more uniform? I am not clear on any of this or if
it is even important so I would appreciate any guidance that you can
provide!
My understanding is that I want to get the radials at least .05
wavelength above ground so at least 13’ above ground. Is that correct?
Tnx & 73
Bob, KQ2M
-----Original Message-----
From: jimlux
Sent: Friday, October 23, 2020 8:44 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 4 square question
On 10/22/20 9:45 PM, Michael Tope wrote:
Bob,
I found this by googling "4 square 8 directions":
https://ncjweb.com/bonus-content/k3lc4squarea.pdf
I think W8JI describes something similar on his website.
73, Mike W4EF....................
and that 4 square handbook from the DF6QV.. He's got all possible boxes
and phasing
http://tm1o.free.fr/4SQ/80m/en_ver_final4-sq_03_04_15.pdf
On 10/22/2020 7:39 PM, kq2m@kq2m.com wrote:
I really want to thank Jim, Jeff, Les, Mike, John and Gary for all of
their help, answers and ideas to which I have been giving a lot of
thought this week. The information gleaned has made me confident of
the new design. Unfortunately there is no way to avoid putting the
4-square elements around the tower so I know that interaction effects
will likely be noticed. Vicious storms have taken down all the other
tall trees that were previously in use to support my 80 meter
4-square.
Note to Jim Lux – I am particularly intrigued by your idea of changing
the feeding of the elements so that I can radiate broadside from the
side of the array rather than on the diagonal since the only trees
that I have to support elements happen to be roughly N, E, S and West,
which, with the Comtek phasing box, would give me radiation N, E, S
and West rather than the desired NE, SE, SW and NW.
The Comtek ACB-4 outdoor box uses the NW element in Pos 1 on the
outdoor , NE (2), SE (3) and SW in position 4 and arranged as shown in
the .pdf:
www.static.dxengineering.com/pdf/comtek_4_square_info.pdf
Which elements (N, E, S, W) would you put in which positions on the
box (so that the 4-square radiates toward the NE instead of East?
How is the gain and F/B and F/S compared to the standard pattern that
radiates diagonally?
Tnx to all & 73!
Bob KQ2MTowerTalk mailing list
TowerTalk@contesting.com
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