Vertical antenna Notes

My Vertical Antenna Notes....

Test antenna is 28 feet tall

Radials are on top of ground

Modeling software is EZNEC+ 4

In general, I conclude that a 28 foot vertical radiator can be useful on 160-20 meters.

As the saying goes, "The devil is in the details"!

The models I have assembled do not take into consideration the Ground system, bandwidth or matching. These parameters do not affect the antenna patterns.

To Do list:

Ground System-

Amateurs must usually make do with much shorter and many fewer radials, particularly on the lower frequencies, but one can often reduce the length of radials and their number considerably without incurring significant loss. Still, the Antenna Book observes that with only two 1/8-wavelength radials (about 17 feet on 40 meters) overall efficiency is not likely to exceed 25%, in which case the difference between a bare-minimum ground system and an “ideal” one might amount to a whopping six decibels or more.

(4-16-2007 Note: There are now 36 radials at up to seventy feet in length for a total of 2000 feet of wire. )

Efficiency (the ratio of power radiated by the antenna to the total power fed to it and expressed as a percentage) can be easily calculated by dividing the radiation resistance by the total impedance of the antenna circuit (i.e., radiation resistance + ground loss resistance + conductor, trap and loading losses of all kinds).[from Butternut- Why Radials]

What ever you do to the 28 ft radiator will affect its matching. I found shunt feeding to be especially challenging.

Bandwidth- Narrow bandwidths make an antenna tuner attractive for non-resonant radiators.

Matching- Extensive experimenting with the TLW program from the ARRL Antenna Handbook (20) has indicated some frequencies are easy to match and some are not so easy such as 1.9mhz. Some of the computed matching parameters are indicated to be quite lossy as well. I ASSUME that a computer driven tuner will exhibit similar losses.