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...

Tom, K1JJ

                     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 half.

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 height.

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.


10) The 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 base.

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 contaminants.

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 copper.

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?

Tom, K1JJ