Vertical Radial Ground Systems
After talking with a number of 160M vertical antenna gurus, I've collected
some great info that may interest some. Hopefully this will help some guys
planning on putting up verticals. It certainly helped set me straight and I've
applied it to my 3 element 160M vertical array.. Remember that this is antenna
talk and prone to opinions and other biases...
Condensed Opinions and
Experiences with Vertical Radial Ground Systems:
1) Ground radials have very little effect on pattern formation. By laying
them out longer or concentrated in favored directions, this will NOT bias
directivity or efficiency in any particular direction.
2) Radials are used to reduce ground losses only. Picture a vertical as one
half of a dipole. RF current normally flows back and forth thru each dipole
Now, like the dipole, the vertical element is one half, and other half is the
Earth soil. RF current does not flow efficiently through average soil. The
copper radials are laid upon the Earth as a "shield" or path to return
(collect) the RF current back to the base. This happens 1.8 million times a
second on 1.8 mhz.
Another way to picture it: The vertical has a large group of long resistors
all around attached to its base extending out. The resistors represent the
Earth soil. Your job is to short these resistors out with wire to produce a
low resistance path back to the base.
3) Very low current flows through each individual ground radial wire since the
total current is divided up amongst many. So, thin copper wire is OK.
4) The best place for ground radials is on the surface, not buried. I find it
very easy to staple the wire down to the grass and let it grow around the
wire... the grass will push it down. Mowing is easy. Best done in the early
Spring or after a short cut mowing job. Take solid #6 copper wire and cut it
into 5" pieces. Bend them in half into 'U' shaped staples and stomp into the
ground holding down the radial every 10' or so.
5) If you use more than one vertical element, tie the two groups of element
ground radials together and terminate them using a common bus half way between
the elements. This saves on wire, reduces parallel resonances, and gets ALL
radials shared for each working element.
6) Some say the height of the vertical is the maximum radial length needed.
But most say 1/4 wave radials are an important minimum no matter what the
7) 50-60 radials appears to be the amount required to get into the "flat" part
of the efficiency curve for fair soil - diminishing returns. 120 radials is
nice, but appears to be overkill.
8) A lamda of about .03 is the maximum distance between radials for
"reasonable" efficiency. This is the maximum "gap" between each radial before
a reasonable efficiency is lost. I believe this means that Earth
currents between the ground radials become a meaningful part of the loss if
this number is exceeded.. By using 60 radials you will easily be within this
parameter when using 1/4 wave long radials. Once the radials are less than
about .025 to .05 wavelength apart at the farthest point (the tips), adding
more wire is a wasted effort. This is 13'-26' apart on 160M.
9) An additional, concentrated short ground screen is a waste. If 60 radials
or more are used, the first 40' or so of the radial field is very dense
already - an additional screen will have no worthwhile effect. I was told
this screen is rarely used at BC stations - and if used, it's usually a
copper flashing material that is used more to keep from tripping over radials
and perhaps to protect equipment placed at the base from lightning.
successful technique of using only 2-4 elevated radials may be overstated.
The jury is still out - many
guys do not agree as to what amount of elevated radials equate to ground
radials. According to some, four elevated radials on HF work fine . Still
others say four have very little shielding effect and are down as much as 3-5
db over a full-blown 120 ground radial system. Four will work for a VHF ground
plane that is essentially in free space, but for HF, the Earth is a major part
of the equation and RF currents must be collected around the vertical in the
near field and returned to the base in an efficient manner. A few elevated
radials cannot do this efficiently simply due to the wide open missing gaps.
Some say that at least 30 elevated radials are needed to do the job of 120
ground radials. Maybe more. Elevated radials 1/8 wave high or higher may be an
exception to this.
My question is this:
If 3-4 elevated radials are equivalent to an elaborate ground radial
system, why do the AM broadcast stations continue to pour tens of thousands
into elaborate 120 radial ground systems when they could hang four simple
elevated wires? Do the pros like to spend money for nothing or are the hams
holding back a valuable secret? HA! Wish I had the answer. Either way, I have
personally installed (60) 1/4 and 1/2 wave long ground radials under each of
three in-line verticals here - I'm happy.
11) Unless 1/4 wave parasitic vertical elements (reflectors and directors)
have their own good ground radial systems they will degrade the expected
gain. Even a few ohms in the base will drop db quickly. F-B will also be
degraded since the element will have less current due to resistive ground
losses to form the proper pattern. They should have as good a radial system as
the main driven element.
12) A symmetrical radial pattern around the base is important! It's just a
matter of collecting RF currents away from the lossy Earth soil. Even a
directional vertical array has energy off to the sides in the near field, as
very little pattern formation is completed close in. All energy in all
directions needs to be collected. The main purpose of the radials is to reduce
losses. IE, the elements radiate in all directions in the near field , so you
need a screen in all directions to intercept current and return it to the
13) Once the ground loses are minimized through a heavy concentration of
radials, it is up to God and the Earth miles away as to how good your low
angle efficiency will be. If your far field ground is poor, a chunk of the
lowest angle lobe will be bitten out, just like Pac Man. Search "Brewster
angle" for more information on this.
14) I've found that #14 insulated PVC SOLID copper wire is great for radials.
It costs $12.77/500' at Home Depot -good deal. Easy to splice into when
connecting interlaced radials to form a grid.
15) When connecting interlaced radials together, bind with wire, solder, then
tape real well and then coat with RTV or some good weatherproofing compound.
The solder will fall apart into a white powder if exposed for long in the soil
without protection. If sealed off, the sealed insulated wire will keep the
copper inside bright and shiny for years...sealed against water and soil
16) When using a single vertical with radials, interlacing or connecting the
radials together with a single wire from radial to radial is a waste of
17) Some feel that adding another wire to help narrow the gap or "fill in"
by forming a 'Y' is useful when the radials are very long instead of
increasing the number.. This applies to the radial areas far out from the
base where the radials become spaced far apart.
18) Radials on 160M should be AT LEAST 100' long. If they are too short,
increasing the number and density will not cure this problem. It's a matter
of covering all areas. Once a certain density (as described earlier) is
achieved , adding more radials the same length is a wasted effort.
19) When using a steel tower, three copper wires connected together at the
top and run down the tower legs to form a "cage", and connected to the base
will insure that tower joint problems will not be a factor.
I suppose the cross sectional area of the steel tower makes the resistance
low enough so that the copper wire does not help in this area too?