Howdy:
Some might be interested in a small, fairly new type of antenna that could be made cheaply, but does take some
effort to tune, but once tuned, you have a small antenna that will work on the lower bands.

The EH Antenna was introduced as small dipole making use of the controversial Crossed Field Theory. One of the conditions for this
mode of radiation is to arrange the magnetic (H) field in phase with the Electric (E) field. The original theory provided by the
inventor was based on feeding the antenna through a 90 degree phase shift network which he claimed shifted the current fed into the
antenna by 90 degrees relative to the voltage across it.


Plans for 40 meter EH antenna:
http://www.qsl.net/vk5br/EHAntenna20_40.htm

80 meter EH antenna:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=9346

Some photos of EH antennas:
http://images.google.com/images?hl=e...Images &gbv=2


--

SeeYaa Harbin Osteen KG6URO

When American Citizens with dual citizenship pledges allegiance
to the flag, to which flag do they pledge allegiance too?

-

chuck wrote in news:1174053226_6783
@sp6iad.superfeed.net:

If the short antenna is matched (i.e., you use a tuner) it will be
nearly as efficient as its longer counterpart. A short vertical antenna
has very HIGH current at its base. Any loss in efficiency is due almost
exclusively to the tuner when operated over seawater. Over land, ground
losses become a more significant factor in reducing efficiency.



Any antenna shorter than 1/4 wavelength has HIGHER impedance and LESS
current. It NEVER has high current at its base. It also suffers from
having so poor an H-field generated without that big current lobe.

A shortened antenna is NEVER anywhere near as efficient as a full 1/4
wave radiator....or more...working against a ground system. Boy, would
AM broadcasters love to have an efficient 50' antenna tower. You'll be
FILTHY RICH if you can make that work!...(c;

If you think running your HF tuner is efficient, you are sadly mistaken.
That tuner is simply a big dummy load on a short whip. It sucks!



Larry
--
Roll up to the long checkout line....
Yell, "ICE RAID!"
It's your turn to load the grocery belt...(c;

"Harbin Osteen" wrote in
:

controversial Crossed Field Theory

Oh, ok...Is it made out of lawn furniture like the Gap antennas that
suck?...(c;

We have a ham in town who is a car mechanic. Someone convinced him if
you put this capacitor in series with his 160M long wire it would make a
super antenna. The poor sap bought it, hook, line and sinker and has
built many versions, to my amusement.

I added a second Texas Bugcatcher center loading coil to my 15' mobile
monster with the 4' across capacitor hat on the trailer hitch of my old
Mercedes 220D, the finest HF mobile car ever built....no electronics
noise. It was about 10PM and I was on 160M around 1850 Khz when I heard
this guy talking to some of his buddies over in MS and New Orleans. I
fired up the modified 650W output Tentec Hercules II and said hello.

One of his buddies, or maybe former buddies now, said, "Bob! That mobile
in Charleston is 20 dB LOUDER than you are!" Bob never made another
transmission....(c;

I love to play with antennas. I always have....

Larry
--
Roll up to the long checkout line....
Yell, "ICE RAID!"
It's your turn to load the grocery belt...(c;

Larry wrote:
chuck wrote in news:1174053226_6783
@sp6iad.superfeed.net:

If the short antenna is matched (i.e., you use a tuner) it will be
nearly as efficient as its longer counterpart. A short vertical antenna
has very HIGH current at its base. Any loss in efficiency is due almost
exclusively to the tuner when operated over seawater. Over land, ground
losses become a more significant factor in reducing efficiency.



Any antenna shorter than 1/4 wavelength has HIGHER impedance and LESS
current. It NEVER has high current at its base. It also suffers from
having so poor an H-field generated without that big current lobe.


Hmmm. You're thinking about the capacitive reactance of a short antenna,
which can be high, and I'm thinking of the radiation resistance, the
real part of the antenna's impedance. When the short antenna is matched,
the capacitive reactance is cancelled by the tuner and you are left with
a radiation resistance that can be as small as a fraction of an ohm. by
comparison, the radiation resistance of a quarterwave vertical antenna
over seawater is about 35 ohms. The base of the antenna is always a
current node on a short vertical antenna: current is a maximum there.
The high voltages (and low currents!) occur at the tops of these
antennas; not at their bases. Where would the current flow to at the top?

If you deliver 100 watts to a short whip, it will radiate as well as a
quarter-wave vertical, assuming the same ground system, etc. There will
be MORE current at the base of the shorter antenna because power = I
squared x radiation resistance. Radiation resistance of a short antenna
is smaller than that of a quarter-wave antenna, so to keep power at 100
watts, I must INCREASE!

I would not be surprised for a 16- or 23-foot whip on a boat to
outperform a 55-foot, sloping backstay antenna at very low angles of
radiation, even with matching system losses. At 7 MHz, for example. FWIW.

A shortened antenna is NEVER anywhere near as efficient as a full 1/4
wave radiator....or more...working against a ground system. Boy, would
AM broadcasters love to have an efficient 50' antenna tower. You'll be
FILTHY RICH if you can make that work!...(c;


Keep in mind that a decrease in efficiency of 70% (1 dB) is needed
before someone at the other end would even notice it. I would imagine
that with reasonable attention to the matching components, an antenna
could be shortened to 1/8 wavelength without any noticeable drop in
signal strength, and without any noticeable change in the vertical
radiation pattern. A 1/16 wavelength whip over seawater might seem
slightly weaker to a distant station than a full quarterwave vertical
over seawater. No quarter-wave antenna with its base on the ground is
likely to outperform a 1/8 wavelength whip over seawater.

The efficiency of a resonant vertical antenna SYSTEM (even with a
radiator that is a tiny fraction of a wavelength long) is the radiation
resistance (a small number) divided by the sum of the resistances in the
system. These resistances consist of losses in the antenna wire, the
ground system, and the matching circuit (which may be inductors and
capacitive hats) x 100 (to get efficiency in %). Over seawater, "ground"
losses are insignificant, and antenna wire resistance is often
insignificant. There are indeed tuner losses, but these can often be
reduced. The point is that the important sourcea of inefficiency are not
in the antenna but in ground loss and matching circuits.

Eventually, an antenna gets to be so short that the losses (or costs,
broadly defined) incurred in feeding power to it are unacceptably high.
Too much power would be lost in the rest of the system. Nonetheless,
that short antenna will radiate all the power that is delivered to it
with high efficiency.

To maintain balance, I would mention that an antenna that is "too long"
(e.g., your 55' backstay on 15 meters) also requires matching and that
will introduce losses. There are not many antennas that will work on
every HF band without matching. Those that do tend to introduce their
own high losses.

With regard to AM broadcasters, it is not for me to say where the
economics, regulatory, and efficiency curves cross, but capacitive hats
on antennas shorter than a quarter-wave are not unheard of on those
antennas.


If you think running your HF tuner is efficient, you are sadly mistaken.
That tuner is simply a big dummy load on a short whip. It sucks!



Tuner losses are indeed significant at lower frequencies with a short
whip. And on most automobiles, ground losses are also significant. Of
course, a seawater ground and quarter-wave whip are not really
alternatives if you're in a car. ;-)


Chuck

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chuck wrote in news:1174139919_4745
@sp6iad.superfeed.net:

Hmmm. You're thinking about the capacitive reactance of a short
antenna,
which can be high, and I'm thinking of the radiation resistance, the
real part of the antenna's impedance. When the short antenna is
matched,
the capacitive reactance is cancelled by the tuner and you are left
with
a radiation resistance that can be as small as a fraction of an ohm.
by
comparison, the radiation resistance of a quarterwave vertical antenna
over seawater is about 35 ohms. The base of the antenna is always a
current node on a short vertical antenna: current is a maximum there.
The high voltages (and low currents!) occur at the tops of these
antennas; not at their bases. Where would the current flow to at the
top?

When a tuner matches a short antenna's reactance and high impedance to,
say, 50 ohm coax, the current to the antenna is very low, in comparison
to the current in the coax at 50 ohms. Most of the current in this
circuit is confined to the series inductance inside the tuner, which
isn't radiated as H-field.

A 1/4 wave vertical over a good ground, like seawater, is closer to 12 to
20 ohms of resistive impedance, if the ground is at the feedpoint where
it should be, not 20' of strap away going down to the bilge. 1/4 wave
verticals have very low impedance, indeed. This makes a very heavy base
current at the feedpoint, if we're lucky, resulting in an impressive H-
field expanding away from the feedpoint at the base, dropping as you go
up towards the open end. A shortened antenna, like an 18' whip on 4 Mhz,
has almost no current at its high impedance feedpoint the tuner must deal
with. H-field suffers awful which causes the E-field to collapse to
match it. It radiates "poorly in all directions", a typical HF mobile
installation.

Many things, some reasonable, some not, can be done to "draw" the current
lobe up the antenna. Some are not practical in a marine environment and
certainly not "boat pretty", so won't be tolerated on yachts. The best
solution is to move the tuning inductor UP the antenna to its middle,
"center loaded". A center-loaded short antenna can be made to exhibit a
very low impedance at its base feedpoint, no where near 12 ohms of a full
1/4 wave vertical, but in the range of 20-30 ohms if the loading coil is
of sufficient size to be efficient, with low capacitance between windings
and low winding resistance, which wastes power turning it into heat. The
antenna appears a little inductive, which is easily balanced by shunt
capacitance at the base. Here's my center loading coil from 80-10
Meters:
http://www.texasbugcatcher.com/cata/tbcspec.htm#6inch
Look at coil #680, which is 6" in diameter on a Lexan form. The white
center insulator is very heavy Teflon. This coil is 4' up a 15' whip
from my feedpoint. I use a large clamp and braided copper strap
connected to the bottom of the coil to tune it by shorting the bottom
turns. Even that creates immense base current at resonance....(c;

On the same webpage, the #480XL coil is inserted in series with the #680,
and the #680 tuning short is used to tune the 15' beast below 3.5 Mhz.
At 1.8 Mhz, this is a VERY short antenna and VERY inductive.

The feedpoint at the car's trailer hitch has two different RF
autotransformers. The HF autotransformer is 10 turns of #10 over a very
heavy ferrite core tapped at every turn. Best impedance match 40-10M
occurs with the antenna tapped 4 turns from ground fed at 6-8 turns, the
coax input tap. 6T at 10M, 8T at 40M. On 80/75M, input is across all
10T, tapped at 5T, an impedance ratio of 4:1, works best. There isn't
enough natural inductance to tune below 3 Mhz, so another ferrite toroid
has 30T of #12, fixed tapped at 22T to operate on 1.8-2.0 Mhz with two
loading coils in series.

The antenna's capacitor hat is 8 stainless steel, about #12 wiresized,
welding rods turned round on the end into a loop to reduce corona, welded
to two stainless washers to hold them tight to a 10-24 whip screwed into
the 3' mast above the one (or two) loading coils. The capacitor hat is
approximately 4' across, and adds capacitive reactance at the top, where
it aids pulling the current lobe up the tuned antenna...instead of at the
base, where it radiates nothing. The capacitor hat and 3' mast above the
coils is removed (1/4 turn quick whip connectors) for operating above 20
meters 14-30 Mhz. Atop the capacitor hat is a cut down stainless CB whip
that creates a resonant antenna on 14.250 Mhz when you short out the
whole 6" coil. The antenna's length and only the capacitor hat resonate
15' to 14.250 by design as that's my favorite ham band. On 20M, VE8RCS
(the northern most amateur station in the world at a Canadian CG base
above the Arctic Circle) reports my mobile in Charleston to be as loud as
any legal ham station they can hear. I used to work them on 20M Packet
quite regularly on 14.105 "Network 105". Their QSL is a prized
posession. Packet, RTTY and the other digital modes are great fun when
traveling with a group of hams to a hamfest...(c;


If you deliver 100 watts to a short whip, it will radiate as well as a
quarter-wave vertical, assuming the same ground system, etc. There will
be MORE current at the base of the shorter antenna because power = I
squared x radiation resistance. Radiation resistance of a short antenna
is smaller than that of a quarter-wave antenna, so to keep power at 100
watts, I must INCREASE!

Nonsense! If it did, every broadcaster on the planet would be buying
50' of Rohn 25 and loading it up at the base....instead of spending
millions on full-sized 1/4 wave radiators like:
http://hawkins.pair.com/wsm/wsmtower.jpg
http://hawkins.pair.com/wcbs_wfan/cbsfan_twr17.jpg
http://hawkins.pair.com/wcbs_wfan/cbsfan_twr14.jpg
(100KW from TWO AM blowtorches is across that insulator)

All you Marine Radio guys need to see this webpage at NSS on Jim
Hawkins' website!
http://hawkins.pair.com/nss.shtml
Take the tour and see why their signal sounds like it does....(c;


Larry
--
Roll up to the long checkout line....
Yell, "ICE RAID!"
It's your turn to load the grocery belt...(c;