In order for an antenna to be a successful radiator of RF, it must radiate
TWO fields, hopefully towards the receiving station. The E-field is an
electrostatic field whos origin occurs at the high voltage points on the
antenna. In our short backstay case, that would be near the top insulator,
which is the highest impedance point in the wire. The H-field is a
magnetic field, 90 degrees physically from the E-field and expanding into
space with it. One field cannot exist without the other over great
distances, so the ideal situation is to have an antenna which creates both
intense E and H fields radiating in a pattern towards intended receivers.

on a vertical wire radiator (whip, backstay) the E field is vertical and
the H field is horizontal.

[whip tip or backstay insulator]
| E field max here, drops to near 0 1/4 wave down the wire
| then rises again to maximum 1/4 wave further down if wire
| is long enough
|
|
|
| H field max at tuner if wire is shorter than 1/4 wavelength. How
| much the field gets drops as wire gets to be less and less of 1/4
[tuner] wavelength.
|
|
[ground] The ground wire and ground create an "image", an imagined
antenna that looks (RF wise) like the radiator would in a mirror,
creating a vertical dipole antenna with the transmitter in the
middle.

The shorter our radiator, the poorer its H-field end-fed with tuner like
this.

As many of you have observed, really short HF whip antennas just suck as
radiators on the lower HF frequencies, getting worse as frequency
decreases. 2 Mhz marine band antennas all sucked because in comparison to
a full-sized 2 Mhz dipole, these antennas were REALLY short. This
"shortness", putting a short whip on top of a heavy tuner to get it to
resonate results in an intense E field from the high antenna VOLTAGE, but
almost no H field as there is little antenna CURRENT at any point in the
wire. The antenna current in this configuration occurs in the big loading
coil inside the tuner, which is causing the high voltage at its output
terminal at resonance. The current in this coil is NOT radiated as H
field, so your signal stinks at the receiver as distance increases, even
though your antenna system is resonant by the tuner's heavy inductance.

Gary Schafer wrote in
:


Why do you think an antenna operates better if it is resonant?


A self-resonant antenna, one that will load the transmitter without any
tuner in the circuit (or bypassed if your tuner will do that), creates the
maximum E and H fields at that frequency, when it is 1/4 wave, and at any
length LONGER than 1/4 wave we can tune it to. Longer isn't much of an
issue on a boat, unless you have room for the 107', quarter-wave tower on
old 2182 marine HF emergency channel. Our antennas are always shorter,
except above 12 Mhz where they become more reasonable in length.

The amount of H-field it creates as a too-short wire is also VERY dependent
on how much RF current we can make run to the ocean through its grounding
system. Great grounding, lots of current. Poor grounding, poor current,
poor H-field creation. E-fields are easy to make with tuner inductors. If
you'd like to see the effect of BIG E-field creation, go to my ham radio
callsign website on http://www.qrz.com/callsign/W4CSC and look at my
picture. I'm holding the bottom half of a 300 KV RF feedthrough insulator,
a souvenir of Reverend Stair (Overcomer Ministry's nut who broadcasts 24/7)
from his pirate radio ship that was temporarily docked in Charleston before
the FCC came to confiscate the 70KW HF transmitter that blew the hell out
of this insulator when it flashed over right above my head! MOST
impressive blast inside the fish hold of an old Canadian fishing trawler
where the transmitters were mounted. E-field is that big black arc down
the side of the porcelain...(c; 70KW on 41 meters is lots of fun. I love
high powered transmitters. "POWER is our FRIEND."

Sorry, I wandered off.....

Now, we hams have other solutions than this crappy tuner at the base of
your whip.....

Marine radio does what it does because it's quick and dirty (not to mention
yacht pretty with all its whitey fiberglass or stealth backstays). Tuners
are NOT a good thing, like this. We try not to use tuners on mobile HF
antennas on ham radio. Let's look at some that tune the ANTENNA to self-
resonance to create big H fields.....

http://www.texasbugcatcher.com/cata/tbcspec.htm
Henry Allen, K5BUG, has always produced the finest "loading coils" for ham
radio and other HF mobile antennas on the planet. My mobile antenna
configuration has two of them, but only when I'm operating in the 1.8-2.0
Mhz ham band BELOW the 2 Mhz marine band right on top of the AM broadcast
band. Above that band, I only use the #680 monstrous coil to tune an
antenna I designed 25 years ago that DRAGS THE CURRENT UP THE ANTENNA. The
antenna is 15' long, because the damned highway department says that's as
high as a truck can be. There are two ways of getting more CURRENT up the
antenna....put the antenna tuning coil about halfway up the length of
it...or...put a capacitor hat near the top of it in the E-field area. The
effect of doing this makes the antenna ELECTRICALLY LONGER, a lot longer,
without making it physically longer. My antenna has both! King Hussein,
JY1, the former King of Jordan, told my my signal was as strong as most
fixed stations. I have the QSL card from His Majesty to prove it...(c;
There is no tuner at the base of my antenna. The antenna is tuned to be
ELECTRICALLY, 1/4 wavelength long by adjusting a shorting tap on the huge
coil. Running 650 watts of RF power from a highly modified TenTec Hercules
II linear amp that's not legal on marine radio, the base feedpoint
impedance is about 18 ohms and produces over 6 AMPS of RF current to create
huge H-fields heard on the other side of the planet!

As you can see, no yachtie is going to let me put a 6" coil half way up the
backstay, so we have to put up with poor signals from the damned
tuners...(sigh) Geoffrey's "Lionheart", an Amel Sharki 41, does have
something I want to get modified to simulate the effect of the capacitor
hat of my ham antenna to make the HF wire longer. She has a triatic
between the top of the main and mizzen right over the insulator of the HF
insulated backstay on the main. I propose, if the masts ever get worked
on, to add two insulators to the triatic, near the mast tops, to insulate
it and connect a stainless cable from the antenna end of the backstay
insulator to a clamp in the middle of the triatic, creating a "top hat"
capacitor hat to DRAW UP that H-field current, making the antenna longer by
a good bit, Electrically.

Did this make more questions or answer them?? I love screwing around with
antennas. I've been doing it since before I got my ham license in 1957
when I was 11. Antennas and HF propagation are fascinating subjects....

Larry W4CSC, old 1st Phone w/Radar endorsement when it meant something...
S/V "Lionheart"
WDB6254 366920680