Hi George,
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. Because of
that, there is a tendency to look for that "free lunch".
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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