[Elecraft] Re:Alligators and Bats

[Bill Coleman]

On 1/11/02 2:46 PM, Ron D' Eau Claire at rondec@easystreet.com wrote:

>Elevated radials work better too. 

Actually, they don't.

>If memory serves right, it's been about 10
>or 15 years since some serious engineering effort demonstrated that the old
>formula of 120 radials on the ground did not produce the best or the most
>cost-effective ground system for short vertical radiators. A much smaller
>number of elevated radials can out-perform the old systems.

Actually, what happened is that folks using antenna modelling programs 
discovered this. Their predictions of antenna performance were the same 
or better using a small number of elevated radials rather than a set of 
ground-mounted ones.

However, the reality is somewhat different. The results predicted by the 
modelling programs were not borne out in actual measurement of 
installations.

Turns out the anomaly was an inaccurate modeling of the effects of ground 
in the programs.

>I've read of a number of commercial systems being built or retrofitted using
>the new data for both short wave and broadcast band antennas, but I've not
>seen one yet.

There were a number of broadcast stations that tried this, but they found 
they don't produce the same results as a properly installed set of 
ground-mounted radials.

Basically, if you can put down 30-60 1/4 wave radials (or 60-120 1/2 wave 
radials), their performance converges to virtually the same as having a 
solid sheet of conductive material. 30-60 1/4 radials on the ground will 
out-perform 4-8 elevated radials.

However, if you can only have 4 radials, you may be better off elevating 
them.


Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901