Tom, W8JI, has written, in part:
>"This "radial stuff" goes on and on. Probably the main reason it continues
>is few of us like to do a lot work or spend a lot of money. "
Well I have just recently purchased 10,000 feet, 10 spools
of #16 solid copper radial wire; several hundred dollars.
Now I can't use it. I have been "invited" to remove my
six (!) verticals from the ratty, vine infested, moderately
steep ravine side location just behind my QTH. This land
has gone unused for mellinia; now has been leased from
the Plantation by a fellow who wants to fence it, and
pasture horses there!!! Had I known, I probably could
have also leased it last Spring for $15 per acre per year,
thats what the going rate is for land of no use to the
plantation estates, who will NEVER sell the land!
Anyway, I will flat out loose any chance of having 160
and 80 meter verticals again; well maybe he 80 here
in house lot size yard. But the others must move up
to the upstairs deck area on the roof of the house.
My verticals are all Gladiators, and six of them will
be mounted as triple banders: see Meyers web site
for info on same:
http://www.primenet.com/~bmyers/triple.htm
A photo is shown of exactly what I have up on the roof now
for the 10, 15, and 20 meter bands, mounted on a single
Radio Shack push up pole. The feed point is about 22 feet
above the soil level surrounding our home. The ends of the
six radiasl (two only per band now) are near roof level, or
around 12 feet or a bit heigher above the soil level, but of
course from a few inches to two or three feet above the
rood shingle levels. Shingels are a cement composition
type called "Hardishakes" they survived hurricane Inike
a few years ago. Lost none of them, except to breakage
via flying timbers from a neighbors home which the winds
blew apart!
Now, if I read L. B, Cebik's web site correctly, see:
http://funnelweb.utcc.utk.edu/~cebik/vdgp.html
Title of the page is:
"Vertical Dipoles and Ground Planes
What Antenna Modeling Reports
L. B. Cebik, W4RNL"
LB makes no real conclusions about verticals elevated
a significant percentage of a wavelength over the
ground plane; whether artificial or actual earth;
his remarks are mostly about the modeling
and relevance to the real world, pr actiually,
the lack thereof.
LB's is the most complete modeling discussion of
vertical dipoles over ground planes I have seen. Note,
he does not discuss 1/4 wave verticals over ground planes,
but is interesting anyway.
LB also references another study by Rick, N6RK of ground
screens beneath some 20 meter verticals, both 1/4 wave
and half wave in length; see: http://www.karlquist.com/
His paper is in .pdf format, so the Adobe Acrobat reader will
be needed to have a look at his work.
Rick seems to conclude that a vertical over a good ground
screen, some 0.4 waves above, performs no better than
a horizontal dipole at 0.5 waves high. Therefore, he decides
never to use them above 40 meters. This conclusion is
drawn from his tests at 20 meters.
Now I will soon have 7 verticals, from 40 on up through the WARC
bands to 10 meters all up on the roof; six bands as Gladiator
triple banders as mentioned, plus the full length, 33 foot tall
40 meter 1/4th wave vertical. All will have resonant elevated
radials up there, two per band.
Now the question is: should that be the way I go, or should I
try to create a dense ground screen up on the roof using
a lot of my 10 spools of 1000 feet each of the #16 copper
wire. Lots of wire spoking out in all directions from just
below the elevated feed points of the 7 Gladiators? I
believed that I had read somewhere among LB's papers
that doing so would be of no benefit to the vertial's
efficiency, but now I can no longer find the particular
sentences I seem to recall, oh well, will copy LB,
perhaps he can confirm or deny, hi.
Any thoughts about my present situation woulb be
greatly appreciated; I have the option of returning
the 10 spools of copper wire, so must decide soon!
I also appreciate all the advice I was given, particularly
by Tom, W8JI, about how to deal with the verticals
when they were out among the vines; but, alas, now
all has changed.
Happy Holidays and 73,
Jim, KH7M
On the Garden Island of Kauai
>
>The long and short of all this is the only thing that proves an efficiency
>increase or change is a field strength comparison of the same antenna with
>only a ground system change. You'll see that has NEVER been offered in any
>of the articles on radials in recent years.
>
>Since none of the articles measure the only thing that means anything (FS),
>they are just pure conjecture and should not be taken as proving anything.
>
>I have measured systems both ways three times. Once at a broadcast station,
>once in Conyers GA, and once here in Barnesville GA. The soil in Conyers
>and at the BC station were similar, rocky with little topsoil. In both
>cases the difference was about 6 dB when 60 radials contacting soil
>replaced the small elevated systems. In Conyers, I elevated the 60 radials
>and also laid them on the ground. There was no conclusive change caused by
>radial height changes when 60 radials were used.
>
>Here in Barnesville the results repeated, even though the soil has almost
>no rock and is fairly good pasture land. Based on my measurements, my reply
>is:
>
> > Is it permissable to have both elevated and ground radials?
>
>Yes. But with only a few radials (less than about 8 radials per antenna)
>any radials contacting or very near earth will reduce system efficiency.
>
> >Does a ground rod at the juncture of the radials hurt or hinder?
>
>With less than about 8 elevated radials, a ground rod connected at the
>common junction of radials absolutely hurts FS! That is a simple
>measurement. I added a jumper connecting three six foot (or so) ground rods
>to the common point of the radials, and measured a quite noticeable FS
>loss!
>
>>Should the coax shield be left "floating" to the radials or grounded?
>
>With a small elevated system, the shield absolutely must float off of any
>ground connection along with the radials for maximum efficiency. The
>feedline needs a choke balun to prevent current from flowing down the
>outside of the shield. Keep in mind even when I did that, efficiency was
>still not good compared to the same system with more radials.
>
>> Does it help to tune the radials with a meter such as an autek or doesnt
>it matter.
>
>I tuned the radials I had, because the velocity factor in the wire is
>reduced by ground losses. I had no idea how much the added loss of the soil
>would change the Vp in the wires. A resonant radial wound up being a bit
>shorter than 234/f. I tuned my radials by using opposite pairs as a
>temporary low dipole.
>
>> On short elevated radials does it help to load them with a coil?
>
>It doesn't help at all from one standpoint. It is no different that adding
>a coil to the radiator. Remember the feedpoint is in series with the
>antenna and the radials. Which side of the feedpoint the coil goes on makes
>no difference at all, if the feedline is isolated with a choke balun.
>
>If the feedline is NOT isolated with a choke balun, coil location affects
>efficiency and resonance. The coil belongs on the radials. But in this
>case, efficiency suffers even more because the ground path through the coax
>to earth ground adds loss.
>
>The poorest antenna I measured had four 1/8 wl radials carefully resonated
>with a high Q (Q>400) inductor. It was the most critical for feedline
>grounding (or ground rod grounding), and even when isolated as much as I
>could muster with two feedline chokes never equaled or exceeded two or four
>elevated full sized radials. It also had less bandwidth.
>
>Four elevated radials in an optimized system was about 5 dB down from 60
>radials just laying on or buried in the earth, and with 60 radials I didn't
>need to worry about grounding the radials.
>
>This doesn't prove elevated radials can never "work", it just proves they
>didn't work efficiently here (and at two other locations) no matter how
>much care I put in the system..... unless I used more than 20 or 30
>radials. I believe the military tested elevated radials (as reported by
>N7CL) and there results were almost exactly the same as my results.
>
>A W0 on 40 meters also reported he replaced an elevated system at a BC
>station in Indiana, and found the same thing as I did. He said they had to
>explain to the FCC how they suddenly picked up several dB in FS from a
>system (the elevated system) that was supposed to be perfect. The BC
>station I replaced radials at used six elevated radials per tower, and
>gained between 3 and 7.5 dB at all the field proof points after the change,
>despite the fact it was represented as 100% efficient when it used the
>elevated system.
>
>73 Tom
>
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