[Elecraft] EH antenna??

[Ron D'Eau Claire]

> What's an EH antenna?
> 
> Regards,
> Helm.  WB2ADT  [K2, 2698]

I don't pretend to be an antenna engineer so when I first heard about
them I went looking for information. 

There's what claims to be a detailed description at
http://www.eh-antenna.com/documents/EH_ANTENNA_DEFINITION.pdf

I don't know if these are the originators, so I can't say if the is the
definitive write up on the subject.

I read I carefully and decided I was an ol' hound dawg chasing my tail.

It divides antennas into two categories, Hertzian and EH. The "EH" of
course is the "new concept". 

They forgot (or didn't know about) Marconi antennas, which were the
first and still possibly the most common antenna in use for
communications today. A Marconi, of course, is fundamentally a 1/4 wave
radiator that uses an "earth image" to resonate. A Hertzian antenna is,
fundamentally, a half wave radiator that operates independently of the
earth. The Hertz is the oldest antenna, of course, being what Hertz
himself used to demonstrate the propagation of electromagnetic waves.
The problem is that Hertzian antennas become very big at low
frequencies. Hertz used a half-wave loop at about 50 MHz for his
experiments. 

Marconi invented the idea of using a 1/4 wave radiator working against
ground because he needed, to get the range he wanted with the technology
available to him, to work at wavelength in the hundreds of meters. Makes
for a HUGE loop to carry around. 

Back to the EH, then. Reading the description, it claims to be a Hertz
antenna with a special phase shift network added. This phase shift
network exactly offsets the "j" factor in the input impedance to the
antenna. 

That's good. But it's not new! It's what we ALL do when we adjust an
antenna or the ATU. When we adjust an antenna (or our ATU clicks us to
an SWR of 1:1) all we are doing is compensating for the inherent "j"
factor (capacitive or inductive reactance) so the antenna will take
power efficiently. 

If you don't recognize the term "j-factor" it's the complex or reactive
part of any impedance. An impedance is written as R j(X) where "R" is
the resistive part of the impedance and the "X" is the reactive part.
For example, if an antenna is exactly 1/2 wave long and way up in the
air (several wavelengths above ground) it will have an impedance at the
center of about 75 j0 ohms at "resonance". That is, the impedance is
purely resistive (75 ohms) and the reactance is zero, so it will take
power from a 75 ohm generator (transmitter) very efficiently. IF the
antenna is too long, it will show inductive reactance. If it happened to
show 50 ohms of inductance, we would write the impedance as 75 j+50
ohms. (Note the plus sign. Inductive reactance is positive and
capacitive reactance is negative.)

The reactance causes the current and voltage to no longer be in phase.
If they are no longer in phase, not as much power is being transferred.
(Power is the product of the voltage and current. If the voltage peak
and current peaks do not occur at the same instant, their product will
be less than if they did). 

So the challenge is to get the voltage and current back in phase. We add
50 ohms of capacitive reactance to the circuit. We add 75 j+50, our
antenna, to our ATU providing 0 j-50 and the sum is 75 j0 or a perfect
"match". 

Our SWR meter is happy, our r-f gets out, and we are happy.

That's what the EH antenna description says it does, so I quite certain
that it works very well. 

The only thing is, I can't figure out what's new in all of that. I've
been doing that for 50 years, and folks since Marconi had been doing
that for over 50 years before I first loaded up a wire with r-f. 

Perhaps someone can enlighten all of us about what is different about an
EH antenna that we don't all have. 

Ron AC7AC
K2 # 1289