[Elecraft] My Experiences with EH antennas on 20 meters

[Charles Greene]

Vic,

Tnx for comments.  The antenna has a high impedance; for purposes of the 
network calculation, an antenna load of 30 -j994 ohms is used which was 
empirically determined.  This value is dependent on the capacitance between 
the elements which is on the order of 10 pF.  It is matched to 50 ohms with 
a simple L network which also functions to produce the 90 degree phase 
shift.  The elements in two of my antennas are 2" diameter copper tubes 
7.5" long, and 1" Al or Cu tubes in the other two, so the loss in the 
elements is very low, and probably is dielectric in nature rather than 
ohmic.  You can calculate the network for the phase shift and also the loss 
in it with the KM5KG network design program.  The loss in the network is on 
the order of 3 to 5%.  If you put the parameters of the antenna in the 
right part of the KM5KG program, you get 50 ohms at the input.  I have 
measured the return loss of the antenna up to -45 dB using a return loss 
bridge, which corresponds to a SWR of less than 1.02:1 at resonance.  To 
tune the antenna with a transmitter, I use ten watts and connect a OHR set 
up to read reverse power, finally on the 100 mw scale.  Of course, this has 
nothing to do with the performance of the antenna, but just measures how an 
L network can easily match the antenna impedance to 50 ohms.

Of course the antenna beam is reflected from ground or in my case, the sea 
water for the semi-circle starting at 180 degrees and working around to 
North for 5 miles or so until you hit land, but the radiation starts out 
like it is coming from a vertical beam about 10 wide without side lobes, 
and goes on from there.  You can't model the antenna, but a normal 1/4 wave 
vertical antenna on my sea wall modelled with EZNEC using a sea water 
ground shows a narrow beam width at less than 10 degrees vertical angle in 
the far field.  Using a medium ground at the other directions in EZNEC I 
would estimate is reasonable accurate as concerns the far field vertical 
beam pattern.  I didn't mean to mislead you in this respect, I and probably 
was not exactly correct in my statements.  The antenna just is relatively 
immune from ground losses in the near field as it doesn't use a ground 
return, but performs like a normal vertical for reflections and ground 
losses in the far field.

The Hustler is a trap vertical and I have a radial field consisting of 24 
radials of 480 feet #14 wire total.  The radial field is not nearly enough 
on 40 and 80, but it is reasonably good, and the performance of the antenna 
is reasonably good on 20.  I estimate it has above average performance for 
a vertical, and it also benefits from sea water reflection in the fresnel 
zone, as it is 50' from the salt water.  It beats my G5RV on 20 but not on 
40.  I also compared The EH antenna with my G5RV, which is really an apples 
and oranges comparison as there are differences in directivity in both 
horizontal and vertical patterns between the vertical antenna and the 
horizontal antenna.  The point is, I did not just compare the EH antenna 
with a poorly performing vertical antenna.

I won't try to go into the theory of operation of the antenna, and if 
anyone wants to say these guys don't know what is going on precisely, you 
are correct.  I just concentrate on performance and factually report my 
experiences.  It appears use the same theory as the Cross Field Antenna, 
CFA, discussed in the Antennx on-line magazine, although the physical 
properties of the antennas are different.

There is a lot of information at the US EH Antenna web site:
www.eh-antennas.com     Also of interest are some of the links found 
there.  One additional link is: 
http://hem.bredband.net/sixens/EH_ANTENN_SM5DAJ.htm        which has links 
to other European sites.  The Europeans are ahead of US hams in a lot of 
respects concerning EH antennas, particularity those in Sweden and Italy.

I guess I better get off the subject or Eric will throw me off the 
reflector.  If I get flames, I need to address them, but I do not flame in 
return.  Any questions, please ask off line.



At 07:55 PM 2/23/2003 -0800, you wrote:
>Charles Greene wrote:
>
> > The EH antenna really works, well.  It's efficiency, as an antenna, is on
> > the order of 95%, as compared to about 75% for the full size 20 meter
> > vertical with elevated radials I build last summer, and few percent for a
> > short fat dipole the same size but just loaded with a loading coil because
> > of the high losses in the loading coil.
>
>How did you determine this?  Do you know the radiation resistance?  I suspect
>the radiation resistance is very, very low...and as a result, so is the
>efficiency.
>
> >  On 20 meters, its beam width is on
> > the order of a few degrees, concentrated near the horizontal.
>
>Absolutely not true, unless you have it on your boat over salt water.  The 
>fact
>that the antenna does not use the ground as a return path (since it is a
>dipole), does NOT imply that the relative power at various angles is not
>determined by ground reflections.  In this respect it's no different from the
>Cushcraft, Gap, etc. vertical antennas.
>
> > As it needs
> > no ground, its ground losses are very low. It doesn't need a return ground
> > path that includes the lossy earth ground.  One of my EH antennas for 20,
> > (I have four) has a bandwidth of 200 kHz, and it achieves this without
> > resistance or other tricks.
>
>Well, it has resistance -- the RF resistance of the antenna elements as 
>compared
>to the radiation resistance.
>
> > However, the EH antenna beats my
> > relatively good Hustler 6BTV in gain consistently by 2 to 3 dB.
>
>My guess is that the Hustler (for those who aren't familiar with it, it's a
>short trap vertical monopole, which needs a ground system) is set up without a
>radial system of any kind, or a very rudimentary one.  Am I right?
>
>Vic K2VCO


73, Chas, W1CG
K2 #462