We begin with underground radials.

I will show you a graph of the number of radials and the length of the radials that should be quite acceptable. I found it at the STEPPIR website while researching this topic. It was created by Brian Edwards N2MF and used here with his permission. This graph was originally shown in the June 1985 QST article "Radial Systems for Ground Mounted Vertical Antennas." www.steppir.com/pdf/radial%20systems%20for%20vertical%20antennas.pdf

All these radials may seem mildly exccesive, but a good ground is an essential part of a vertical antenna. It is not possible to have too many radials.

The vertical radiator and the radials in the ground form a giant capacitor which supplies a "flow" of electrons in the antenna system, and it helps keep the Take-Off angle as low as possible. This is essential.

Are you ready for another graph? This one comes from that same Stepper website as above. This one says that the more radials you have, the efficiency goes up. That is a very good thing. I will discuss "efficiency" in a moment.

The question of "efficiency" in a vertical antenna.

The "efficiency" of this antenna can be calculated by a simple algebra formula, but if you are one of those who can not remember a darn thing about your high school algebra, fear not. Remember that I will do all the math and I will be happy if you just nod your head and say things like " That is what I thought.", or "I knew that", or "Sure, that makes sense." All you really need to do is to remember the conclusion of the discussion, and I will make that clear.

The efficiency is found by dividing the radiation resistance by the sum of all the resistances in the antenna and ground. Then this number is multiplied by 100 so efficiency can be calculated in percent.

Efficiency = Radiation resistance * 100 / sum of all the resistances in the antenna and ground.

In the case of the perfect vertical antenna, where all the ground resistances are zero Ohms,the formula will look like this...

Efficiency = 36 Ohms *100 / 36 Ohms + 0 Ohms = 100 percent

A perfect antenna should have an efficiency of 100 % shouldn't it? 100% efficiency means that 100 % of your output power is going into the air where it should be going, and it is not being used to heat the earth. The point of this discussion is that the only way you can have a perfect antenna system with 100 % efficiency is to have a perfect ground system.

Do not skimp on your ground system. Using both of those graphs, to get 80% efficiency from your vertical quarter wave antenna, you need about 55 radials that are about 0.288 wave lengths long. Using these numbers, an 80 meter vertical will need over 4000 feet of wire for the 55 radials that are about 74 feet long. That is a whole lot of wire.

Vertical antennas that have grounded radials are not cheap to build if you want one that is efficient and has a low Take-Off angle. Both efficiency and a low Take-Off angle are the key to having a FANTASTIC antenna. A good quarter wave vertical with buried radials can often out perform a dipole that is way up in the air.

Go to the SWR section next. Simple SWR Theory.. Not difficult to understand.

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