[TowerTalk] Resonating Raised Radials

[Eric - VE3GSI]

All you vertical experts,

Lately there has been a lot of great chatter on this reflector on radials,
raised or otherwise. Since I am in the planning stages of a 40 meter raised
vertical, not all that high but the base of the vertical element will be
around 20 foot above ground. Depending on final installation the number of
radials will be from four to six.

>From what I remember, the formula used for length of radial is 234/Freq x
1.04.  Or simply put, calculate for 1/4 wave and add 4 percent.

My question. Is the above formula valid, or how do you fellows calculate
length of the radial element?

Next, as we all know the surrounding environment can skew antenna formulas.
So how do you measure radials to assure they actually resonate on the
desired frequency. I have some thoughts of my own but I would like to hear
from others.

Eric - VE3GSI