EZNEC4 computes the antenna currents. Knowing the voltages would be
interesting. Unlike the feeder line where the voltage or current are
easily determined from the characteristic impedance, the line
parameters, and the terminating impedance, how do you
determine the antenna voltages? First blush says, uh, 377ohms relates
the voltages and current, but that's in free space. The antenna has
radiation, inductive, and electric fields (well, the radiation field
is actually the transverse electric field component), so how does one
go about getting the voltage as a function of antenna position (EZNEC
current). I'm sure the answer is obvious but I'd appreciate
confirmation (of an answer and my clouded intellect).
Thanks.
jimg
Oregon
USA

jimg wrote:
EZNEC4 computes the antenna currents. Knowing the voltages would be
interesting. Unlike the feeder line where the voltage or current are
easily determined from the characteristic impedance, the line
parameters, and the terminating impedance, how do you
determine the antenna voltages?

You don't. Voltage is a measure of the potential between two points.
When those points are separated in space and in the presence of a
changing magnetic field, which is the situation near an antenna, the
voltage you would measure depends on the path you take between the two
points. Crudely and not completely accurately put, it depends on how you
orient your meter leads.

First blush says, uh, 377ohms relates
the voltages and current, but that's in free space.

No. 377 ohms is the ratio of E to H field of a plane wave in free space.
It isn't the ratio of any voltage to any current anywhere. There is no
current in free space, and voltage depends on the path you take, as I
said above.

The antenna has
radiation, inductive, and electric fields (well, the radiation field
is actually the transverse electric field component), so how does one
go about getting the voltage as a function of antenna position (EZNEC
current).

You don't. It's not possible. Which is why EZNEC doesn't do it.

I'm sure the answer is obvious but I'd appreciate
confirmation (of an answer and my clouded intellect).
Thanks.

Roy Lewallen, W7EL

Roy Lewallen wrote:
The antenna has
radiation, inductive, and electric fields (well, the radiation field
is actually the transverse electric field component), so how does one
go about getting the voltage as a function of antenna position (EZNEC
current).

You don't. It's not possible. Which is why EZNEC doesn't do it.

The current reported by EZNEC is the net standing-wave current
(for standing-wave antennas). That current is associated with
the standing-wave's H-field which can be measured. The standing-
wave also has an E-field. Is there any way to measure the magnitude
and phase of the E-field? I vaguely remember a florescent light
bulb being turned on by the E-field, glowing brightest at the
tip of a mobile antenna.
--
73, Cecil http://www.qsl.net/w5dxp

yep, that was silly, what was i thinking about?!?!
i guess what i was really after was the peak E field near the
antenna.actually it's there in the NF Tab...just have to figure out
how run/plot the result...

anyway, thanks... i still can't believe that's what I asked for...like
i forgot what a line integral was for...

ok, bye

jimg wrote:
EZNEC4 computes the antenna currents. Knowing the voltages would be
interesting. Unlike the feeder line where the voltage or current are
easily determined from the characteristic impedance, the line
parameters, and the terminating impedance, how do you
determine the antenna voltages?

You don't. Voltage is a measure of the potential between two points.
When those points are separated in space and in the presence of a
changing magnetic field, which is the situation near an antenna, the
voltage you would measure depends on the path you take between the two
points. Crudely and not completely accurately put, it depends on how you
orient your meter leads.

First blush says, uh, 377ohms relates
the voltages and current, but that's in free space.

No. 377 ohms is the ratio of E to H field of a plane wave in free space.
It isn't the ratio of any voltage to any current anywhere. There is no
current in free space, and voltage depends on the path you take, as I
said above.

The antenna has
radiation, inductive, and electric fields (well, the radiation field
is actually the transverse electric field component), so how does one
go about getting the voltage as a function of antenna position (EZNEC
current).

You don't. It's not possible. Which is why EZNEC doesn't do it.

I'm sure the answer is obvious but I'd appreciate
confirmation (of an answer and my clouded intellect).
Thanks.

Roy Lewallen, W7EL

jimg
Oregon
USA