On 10/4/2015 5:08 PM, Jeff Liebermann wrote:
On Sun, 4 Oct 2015 15:24:39 -0400, rickman wrote:

On 10/4/2015 1:36 PM, Jeff Liebermann wrote:
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:

I would like to see some numbers. It is a ground plane with 4 radials
(typical). Free space.

I just noticed the contradiction. You can't have a grounded antenna,
or a ground plane in free space, where there is no ground. Also, as
Jim mentioned, ideal antennas in free space have no dissipative
losses. Try again please.

Why not?

Because a free space model is defined as the absence of a "real
ground", "earth ground", or something sufficiently away from the rock
that you're standing on so that its influence is very small on the
model. That's usually measured in wavelengths. Offhand, anything at
least 10 wavelengths above the nearest ground structure (ground,
trees, buildings, etc) can be ignored. For VHF/UHF, that's a fairly
small distance. For HF, much longer.

I don't know why you are talking about "a real ground" when the context
was a ground plane antenna.

"It is a ground plane with 4 radials (typical). Free space."

Clearly that can exist. You said you can't have a "ground plane". The
antenna has a ground plane no matter where it is.


Is not the ground just the other terminal on the antenna
connected to the radials?

Nope. Which radials? The radials in a common "ground plane" antenna
are certainly not considered an "earth ground".

No one but you is talking about an "earth ground". The comment was
simply about a ground plane antenna in free space. I don't think the
name "ground plane antenna" requires the antenna to have any relation to
an earth ground.


However, the buried
counterpoise that forms the other half of a monopole antenna is
certainly an earth ground. Note that I would need an NEC4 runtime to
model a below ground radial counterpoise system.

Ground doesn't have to be earth ground or
anything else. It is just a defined reference point.

I think the problem is too many definitions of ground here. In my
world, "earth ground" means just that. It's the rock you're standing
on. A "grounded" antenna, is one that uses the earth as the
counterpoise. A "safety or lightning ground" is a path for
atmospheric electricity and does not usually enter in the
calculations.

But no one said anything about an "earth" ground except you. A "ground
plane" antenna is the topic. No one else said anything about a
"grounded" antenna.

Have you had too much coffee today?

--

Rick