Hello,
a big name in the antenna manufacturer say in the brochure of their vertical
antenna: "minimum recommended radial requirements: at ground level, 8
radials of 0,1 wl each calculating the lowest operational frequency. Above
ground, 2 radial cut for the specific frequency for each band of operation."

Assuming a operational frequency e.g. 7 MHz, at what height from the ground
one can consider the antenna mounted "above ground" ??

TIA and 73,

-.-. --.-

On Dec 21, 5:55*am, "-.-. --.-" wrote:
Hello,
a big name in the antenna manufacturer say in the brochure of their vertical
antenna: "minimum recommended radial requirements: at ground level, 8
radials of 0,1 wl each calculating the lowest operational frequency. Above
ground, 2 radial cut for the specific frequency for each band of operation."

Assuming a operational frequency e.g. 7 MHz, at what height from the ground
one can consider the antenna mounted "above ground" ??

TIA and 73,

-.-. --.-

Almost any height, being as the radials will need to be resonant
to work well. The only difference is the number of radials required
to equal a certain number ground mounted decreases as you
get higher off the ground.
But you have to think in terms of wavelength. What might be fairly
elevated on 10m, which almost be on the ground at 80m.
Say you compare to 120 radials on the ground, which is pretty
much a perfect ground within practical limits.
At 1/8 WL, you might need 60 radials to equal the 120 on the
ground.
At 1/4 WL, you might need 8-10 radials to equal 120 on the
ground.
At 1/2 WL, you can use 3-4 radials to equal 120 on the ground.
On 10m, 1/2 WL is only about 16 feet off the ground.
On 80m, 1/2 WL is about 120 feet off the ground.
In the past I've used a full size quarter wave ground plane on
40m at 36 ft, which is slightly over a 1/4 wave up.
I used four sloping radials. I came to the conclusion that the
system was about equal to a ground mounted system with 60
radials.
Some have speculated that ground planes can be run very low
to the ground with only a few radials, and still be nearly as
efficient as a ground mount with 60-120 radials.
I'm not buying it. There is no free lunch in this regard. :/
If the vertical is elevated, but just barely, count on using
almost as many radials as the ground mount for the same
amount of ground loss. There will be a slight decrease in
the number needed, but not by a large amount.
You will need 1/4 wave radials if elevated. They must be
tuned. Ground mount, it doesn't matter. So you can't
use short .1 WL radials if elevated. Only ground mount can
you do that. Elevated, they need to be .25 WL, .75 WL,
etc.. They have to be resonant, or otherwise they will be
fairly useless.