antenna-theory.com

[PatrickC]

Hi, Need experts. So much misinformation abounds.
Have a fiberglass (nonconducting) 42 ft sailboat with a ICOM-802 ssb AT-140 tuner 150 watt PtoP
Hooked ground output of Tuner via 4 inch wide copper foil to grounding plate thru hull to sea water (2.5 ft length) instead of putting copper foil all around inside the inside hull.(capacitive ground)

Hooked high voltage antenna output of tuner to multistrand tinned GTO-15 high voltage neon sign wire about 55 ft long. I raise this up and out the hatch keeping it as far from metal as possible. Raising via Halard (rope) to within 3 ft of top of mast (57 ft above sea level)

This is a monopole antenna? acts as a 1/4wave dipole? uses the conductive sea water as the ground plane/radial?? So a virtual image of the upper radiating element is formed in the sea water around my boat? Vertically down? But sea water does not conduct HF (say 10 MHz very well???) How does this work? The Far Field Fauenhoffer Field has reflection angle to allow launch of the Sky wave to the ionsphere at good angles? I get good signal reports. But want to understand how this works????

Please explain how this really works? I get results but want to optimize.
Could I just hook the TUNER OUTPUT RF 1.5 amps at 900 volts to my 60 ft tall aluminum mast via a stainless steel support wire? Current at termination would be near zero? but Voltage would be high? Need insulator? Could I fry my delicate wind instruments etc.?

Thanks

Patrick in Delaware

[PatrickC]

The Monopole is in theory a half wave dipole with one leg grounded to the sea water. The only emitting leg is above seawater. So a virtual leg that is one quarter 1/4 wave in length forms in the Sea Water below my fiberglass boat? This Virtual Leg forms in the conductive sea water. But sea water does not conduct High Frequency well? That is why Subs use ELF to communicate? Only Extremely Low Freqs will propagate in sea water? SO HOW DOES THIS REALLY WORK please????????
At DC the sea water is nicely conductive due to the Sodium and Chloride ions and other ions.

My Dynaplate is a scintered silicon Bronze consiting of thousands of tiny metal spheres melted together to make large surface area. It is 18 inches by 24 inches with silicon bronze gold coated studs through the hull. It is flat against the outside hull in contact with the sea water outside. The studs have gold plated washers and nuts to connect to the 4 inch wide copper foil that goes to the ground terminal of my AT-140 Antenna Tuner. The ICOM 802 High Freq Transceiver has 150 watts output. thru the antenna tuner to the GTO-15 High voltage wire that I run straight up and out the hatch to just below the top of the mast.

Wish I could just use the stainless steel support wire for the mast as my antenna? But it has a metal to metal contact at the spreader 35 feet up and of course at the very top about 57 feet up.

Please help. THANKS

[PatrickC]

Hi,

I just sent these questions via email too: pjbevel at gmail

More details below:

Thanks for answering my questions about feeding 1.5 amps RF at 900v into my Main Mast via starboard stay chainplate with no insulator.

BIG THANKS!

I had tried several times to get an answer to this question. Many of the so called experts totally got it wrong.
See a typical letter below at the bottom of this email. There is so much misinformation out there about SSB installation.

I reviewed and studied dipole antennae theory and I think that I finally understand the concepts well enough now? Maybe not??? Please help.
I am still curious to understand completely. Please bear with me on my silly questions.

http://en.wikipedia.org/wiki/Dipole_antenna






I even tried to review the Elementary doublet and this is where I began to get lost:

Half-wave antenna

Typically a dipole antenna is formed by two quarter wavelength conductors or elements placed back to back for a total length of . A standing wave on an element of a length ~ yields the greatest voltage differential, as one end of the element is at a node while the other is at an antinode of the wave. The larger the differential voltage, the greater the current between the elements.
….this shows current ZERO at ends? But this is for a Half Wave Dipole
Assuming a sinusoidal distribution, the current impressed by this voltage differential is given by:

For the far-field case, the formula for the electric field of a radiating electromagnetic wave is somewhat more complex:

But the fraction is not very different from .
The resulting emission diagram is a slightly flattened torus.


The image on the left shows the section of the emission pattern. We have drawn, in dotted lines, the emission pattern of a short dipole. We can see that the two patterns are very similar. The image at right shows the perspective view of the same emission pattern.
This time it is not possible to compute analytically the total power emitted by the antenna (the last formula does not allow), though a simple numerical integration or series expansion leads to the more precise, actual value of the half-wave resistance:
------=== Quarter-wave antenna This is what I have installed on my sailboat Correct? So the current at the end is zero but the voltage is MAX? So the 1.5 amps of RF is at 900volts potential and max at the end of my monopole? It needs an insulator???.

The antenna and its image form a dipole that radiates only upward.
The quarter wave monopole antenna is a single element antenna fed at one end, that behaves as a dipole antenna. It is formed by a conductor in length. It is fed in the lower end, which is near a conductive surface which works as a reflector (see Effect of ground). The current in the reflected image has the same direction and phase as the current in the real antenna. The quarter-wave conductor and its image together form a half-wave dipole that radiates only in the upper half of space. The sea water MUST conduct the RF for this to work. Does it attenuate the RF more than Air?
The velocity of propagation of the RF in a good copper is 91% speed of light…in sea water????
This link really bothered me: http://en.wikipedia.org/wiki/Antenna_%28radio%29#Effect_of_ground Ground acts as a DIELECTRIC????
At frequencies used in antennas, the ground behaves mainly as a dielectric. The conductivity of ground at these frequencies is negligible. When an electromagnetic wave arrives at the surface of an object, two waves are created: one enters the dielectric and the other is reflected. If the object is a conductor, the transmitted wave is negligible and the reflected wave has almost the same amplitude as the incident one. When the object is a dielectric, the fraction reflected depends (among others things) on the angle of incidence. When the angle of incidence is small (that is, the wave arrives almost perpendicularly) most of the energy traverses the surface and very little is reflected. When the angle of incidence is near 90° (grazing incidence) almost all the wave is reflected.
In this upper side of space the emitted field has the same amplitude of the field radiated by a half-wave dipole fed with the same current. Therefore, the total emitted power is one-half the emitted power of a half-wave dipole fed with the same current. As the current is the same, the radiation resistance (real part of series impedance) will be one-half of the series impedance of a half-wave dipole. As the reactive part is also divided by 2, the impedance of a quarter wave antenna is ohms. Since the fields above ground are the same as for the dipole, but only half the power is applied, the gain is twice (3dB over) that for a half-wave dipole ( ), that is 5.14 dBi.
The earth can be used as ground plane, but it is a poor conductor: the reflected antenna image is only clear at glancing angles (far from the antenna). At these glancing angles, electromagnetic fields and radiation patterns are thus the same as for a half-wave dipole.
Naturally, the impedance of the earth is far inferior to that of a good conductor ground plane -- this can be improved (at cost) by laying a copper mesh.
But sea water is far better than the soil of earth. But not as good as copper mesh??? Does this virtual image of the other half of the dipole appear on the sea water surface or does it radiate out from my Dynaplate just under the water? Even a few inches of sea water would attenuate the RF??.
When ground is not available (such as in a vehicle) other metallic surfaces can serve as a ground plane (typically the vehicle's roof). Alternatively, radial wires placed at the base of the antenna can simulate a ground plane. For VHF bands, the radiating and ground-plane elements can be constructed from rigid rods or tubes.


Patrick



==== a typical letter to an “expert” ====
I just read your wonderful article on SSB/HF antennae/counterpoise installation on sailboats.
Thank you. It was very informative.

Many folks speak very highly of you.

A moment of your time please: Thanks

I have a ICOM-802 open SSB radio
AT-140 tuner and Pactor IIusb with III license

My boat is fiberglass Whitby 42 built in Ontario Canada in 1987
The chain plates terminate in the fiberglass (insulated at bottom)

=========Questions =======================================

NOTE: I am planning on NOT using an insulator at the top.

What if I fed from the chain plate which is below deck 3 feet from the AT-140 tuner high voltage output to an
long stainless steel wire that runs to the top of my main mast. The chainplate has 5 bolts holding it to the fiberglass rib.
Then up thru the deck to a “T” fitting (not too good electrically?) to the Norse fitting and stainless steel wire.
It is held off by one spreader about 35 ft up (metal contact) but total length is about 60 feet plus.
It is of course terminated at the top of my main mast with a metal to metal contact about 57 ft off the water surface.
My main mast is aluminum and rests on 9 thousand pounds of lead at its base. (grounded?)
According to what I have read my tuner will tune so the Voltage/Current standing wave phase has zero potential right at the top?
(no insulator needed?)
This will allow RF to radiate out to space elegantly without an insulator at the very top? Do you agree?

I would use GTO-15 neon sign wire, tinned 17 strand, soldered terminal lug. From tuner to chainplate.
(Why don’t we use Coax here too? RF losses?)
(Why does ICOM not have a wide flat output here too like for the ground? Since HF travels on the surface and sees Inductive Reactance in small round wires?)


My ground out of my AT-140 tuner is a 4 inch wide double strip of copper foil folded to a point to fit on the ground terminal.
(Why does ICOM not have a flat output here? Instead of a stud to affix the wide copper foil?)
Then to a Dynaplate only 2.5 feet away. Using gold plated Silicon Bonze washers/nuts and studs to the dynaplate on two terminals.

Who is correct? So many experts Why? Some other experts suggest radials.
Do I need radials too? 450 ohm ladder antennae wire attached to the ground lug too? Various ¼ wave lenghts?
Instead of wide copper foil for radials.



Regards,

[PatrickC]

http://en.wikipedia.org/wiki/Monopole_antenna
This link describes the Monopole Theory.
Note the ground plane theory. http://en.wikipedia.org/wiki/Ground_plane
....near field reflection point...in my case sea water is reflecting ????


http://en.wikipedia.org/wiki/Mast_radiator This is what I would like to do with one of the stainless steel support wires of my aluminum mast. It is insulated at the bottom due to my fiberglass hull. It is in contact with my aluminum mast in two points. One at the spreader 35 ft up and of course at the very top 57 feet up. The stray RF high voltage may destroy my delicate wind instruments? I do not know? The Radio Freq is at high potential ...I think 900 volts or so? It has an amperage of 1.5 RF amps or so. The Voltage and Current are out of phase? also the standing wave tuned by my AT-140 is not perfect VSWR is maybe 1.2 at best? or maybe worse?

NOTE: the Shunt Fed design in the Mast Radiator article. "Gamma Match"
How does that work? Mast is grounded but High Voltage fed to certain point on mast? will sparking occur?


Radio antenna theory

In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to function as such (e.g., forms a reflector or director for an antenna). This sometimes serves as the near-field reflection point for an antenna, or as a reference ground in a circuit.

There are a variety of ground planes, including drooping ground planes, and flat circular ground plane antennas. A ground plane may consist of a natural surface, such as the Earth (or ocean) (or salt marsh) or an artificial surface of opportunity (such as the roof of a motor vehicle). A ground plane can also be a specially designed artificial surface (such as the radial elements of a quarter-wave ground plane antenna). Artificial (or substitute) grounds (e.g., ground planes) concerns the grounding structure for the antenna and includes the conductive structure used in place of the earth and which grounding structure is distinct from the earth.

Essentially, the ground plane acts as the "missing half" of a dipole two element, half wave long, center fed antenna. It can be thought of as the "return current" path for the radiating antenna. The efficiency of a ground plane can be measured in ohms as the loss component (i.e., fewer ohms are better) of an antenna's total input impedance. In VHF (30 to 300 MHz or wavelengths 10 to 1 meter) used in mobile communications, the metal of a car body begins to act as an efficient quarter-wavelength groundplane. By the upper VHF and UHF frequencies (300 to 3000 MHz), the car or truck body ground plane can be several wavelengths long, making an "ideal and lossless" groundplane.

[roosaw]

A lot of opinions around as to the best way to "ground" your fiberglass boat
This guy went out and and did some measurements. Seems all that foil is a waist of time.
http://www.kp44.org/ftp/SeawaterGroundingFor_HF_Radios_byGordonWest.pdf