Many antennas function because of common mode currents, rather than working in spite of them. Another recent example, appearing in Antennex's compact antenna articles, is a thick stub "vertical" with no counterpoise. All of these antennas become significantly poorer radiators if common-mode currents on feed lines are eliminated. Because the feed line is the actual radiator, NOT the tiny thing they call the antenna.
Misunderstanding or misapplying Maxwell's equations and the principles behind radiation, in combination with missing some very key points of conventional circuit theory, causes problems.
Reviewing these antennas and the theoretical or technical mistakes surrounding them will help us understand how antennas and transmission lines work. With that knowledge, we can build better antenna systems. The fastest and best way to learn is often to look in detail at mistakes! Authors commonly warn users to NEVER choke feed lines with baluns and to "be sure the feed line is straight and in the clear"!
Authors lay blame for RF burns from feed lines or shack equipment on the antenna's "high radiation efficiency", claiming these small magical antennas radiate so efficiently they naturally excite the feed line and equipment more than full-size antennas.
Whether this is a problem is dependent on the radio you use. Some are subject to RF coupling into the audio system, which causes severe distortion while transmitting.
On some field day setups with watt transmitters we have had so much RF on the radio you can get an RF burn. Below we have suggested ways to eliminate the RF coupling problem.
The problem must be severe when a low-power watt radio causes a burn. Like any good salesman, he turns a design shortfall into a feature! According to the author, unwanted RF on the feed line doesn't come from a feedpoint or antenna design problem like it does on other antennas, in this case the unwanted RF appears because the antenna works so well!
H ere's what actually causes RF to appear on a coax shield and radio chassis. RF can only appear on the radio chassis through two methods:.
The antenna, from poor feed line or feedpoint design, can couple to the radio chassis through external wiring or cables attached to the radio.
The radio chassis itself, being large in terms of the wavelength, can actually become an antenna and receive energy from actual desired "over the air" signals.
Many of us have these problems. Click on this link to see one reason why. In this case, we can probably rule out reason two above. It is unlikely the chassis is a large portion of a wavelength long on meters and that the antenna field is suddenly so strong it is "lighting up the house" with RF.I was investigating this special EH-Antenna by collecting information from HAMs who commented the antennabased on their own experience.
In the following, I provide the obtained comments, and at the end I will add my own conclusions, based on detailed study of the theory. The difference between them are worlds This antenna consists of two small antennas, of which one produces a strong E field, and the other a strong H field in the near field.React page scroller github
Both fields radiate and combine to an electromagnetic far field. That's all. The efficiency is that of a small antenna, that means: nothing special. But "everything radiates" and the logarithmic scale in the form of db's make the difference smaller. The result: S9 for ground plane, S for EH-antenna. He named therefore the EH-antenna "an expensive dummy load". Yes, I was reading that, but the EH surely is not a "wonder antenna".Anti terrorist squad shooting apk mod
Comparing the antenna against a dipole at the same location, the EH generally gave 5 to 6 S-points less in transmission as well as in receiption. After intensive tests I decided to pack the antenna nicely into its box and to offer it for sale All this theory is pure imagination without any scientific background or technical know how. Complete nonsense. Update 8. July Here I refer to the document "EH Antenna - Definition, Ted Hart, The antenna is just an open resonant circuit, formed by the capacity of the two "cans" and the coil between them, with a matching section to adapt the feeding impedance.
At the same time, the feeding coax becomes an active radiator which makes, that this combination is radiating more or less I leave it up to you, if you want to call this construction an antenna. However, there are stories about this antenna, where the performance comes close to the power of a dipole. This may be explained by the fact, that the feeding line acts as the main radiator. Some installation instructions specify, that the feeding coax shall hang free and that its length shall be half wavelength or multiple of this.
In this case we end up with a half wave radiator, fed by the EH. Addition August 6th, Writing jokes Is he not telling us big jokes? I would be very pleased to conduct a antenna test with this type of antenna. They told me, it's the 40m antenna. Then I told, that my station is just on the side and I would like to make a radio test with their antenna. Now they began to search all type of excuse, that no test could be performed, at no day, at no time Interesting, isn't it?
And the user reports I received from my packet survey indicated to dB, or even less. Question: Are we not told a big joke by them? Update: 2.This document was prepared to briefly explain the concept. The instantaneous bandwidth of the simplified antenna an equivalent series circuit is related to the amount of capacity and the radiation resistance. It is obvious from the equation that an increase in resistance or capacity will increase the bandwidth. For this reason the EH Antenna uses large cylinders rather than thin wires and a unique configuration of developing the E and H fields to enhance the resistance.
The large cylinders allow the antenna to be small. To be able to pass current through the radiation resistance it is necessary to cancel the reactance of the capacitor. This may be done by adding a series inductance having the same value of reactance at the desired operating frequency.
Now we have a series resonant circuit as shown in Figure 2. For maximum performance we can tap the inductor coil to provide a convenient 50 ohm match to allow use of a coax transmission line.
The complete antenna is depicted in Figure 3. Note that a variable capacitor has been added. This allows the antenna to be tuned over a small frequency range without significantly changing the performance parameters.
However, any shunt capacity in parallel with the antenna capacity will reduce the bandwidth of the antenna and will affect the matching. Note also that a source capacitor is placed in series with the feed line. At the operating frequency the resistive component of the input impedance of the antenna will be a maximum. However, there will be an inductive reactance in series with the resistance which must be cancelled to allow zero reactance to occur at the same frequency as maximum resistance.
This allows the tap on the tuning coil to be set for a virtually perfect VSWR match. This was taken from a set of equations written to define the antenna. Measurements of the completed antenna provide similar characteristics.
Notice that, unlike a conventional antenna, the resistance peaks at the operating frequency. The reactive component of the input impedance goes through 0 at the design frequency if the source capacitor is properly chosen. Due to the changing values of real and reactive components, VSWR also changes as a function of frequency. The bandwidth would increase if the antenna diameter were increased. The 7 MHz antenna in the example has a diameter of 2.This section of the website, which includes several documents, was prepared to provide an understanding of the EH Antenna.
Three additional documents provide more detailed background information to further define the concept of the EH Antenna from a physics viewpoint and also introduce the reader to a new concept in radiation. For some the most interesting aspect of this section will be a new definition of gravity.
These documents are based on a physics concept developed by Vladimir Korobejnikov, a Russian physicist with whom the author of this website has been communicating for several years. It has been a pleasure and privilege to work with him, and we are excited to include his findings on the website.
Korobejnikov presents the view that electrons are in an orbit, as are all things, including heavenly bodies.
The mathematics based on this concept reveals a new concept in radiation. It also explains the apparent motion of heavenly bodies that, until now, has never been mathematically defined. The summation of these documents is a stunning presentation of theoretical concepts of the nature of the universe that have been proven by evidence. To introduce them to others is indeed a very great privilege and an honor. In the future the documents will be presented to scholarly magazines for further dissemination.
Although the EH Antenna is a very simple concept, it is the first practical change in antenna technology in more than years. The EH Antenna was originally developed by trial and error, and now Korobejnikov has provided the theoretical information to validate the concept. We hope you enjoy reading the material. Home About Site Map Contact.Welcome to Antenna-Theory. The goal is to present a comprehensive tutorial on antennas. In the spirit of Einstein: "Everything should be made as simple as possible, but not simpler.
Would you like updates and news for Antenna-Theory. Sign up on the email list. You'll get no spam, and your email will never be shared. Contact Antenna Theory. The work on this website is copyrighted.
It is ok to reference the site material online with an appropriate link to the site, or proper citation if in print form. Copyright Antenna-Theory. Antennas, Antenna Basics, Antenna Gain. In my life, I have found that once I thoroughly understand a subject, I am amazed at how simple it seems, despite the initial complexity. This I have found true for a wide range of activities, be it riding a motorcycle, learning about antennas, or understanding physical phenomena such as electromagnetics.
With that in mind, I endeavor to write this Antenna Theory website in the simplest of all possible manners. Specifically, consider this statement: Complexity is not a sign of intelligence; simplify.
I have found this to a priceless amount of wisdom. In that regard, one need not know the intricacies of Lebesgue integration or complex integrals involving Cauchy residues in order to fully understand Antenna Theory. In fact, most people who focus on the mathematical intricacies of Maxwell's Equations tend to be poor practicing antenna engineers probably because they try to write code or derive integrals instead of put a product together.
The subject of Antennas is best understood intuitively; this is in stark contrast to the methods in University, where complex math pervades every page. I do not think this approach effectively teaches antenna theory. In these pages you will not find rigorous mathematical analysis which only apply in the simplest of antenna cases and are ultimately artificial for the real world ; I will try to state facts and a minimum of math except where necessary.
I also try to avoid making things unnecessarily complicated. But it is simply a measure of how much power is reflected from an antenna. Avoiding unnecessary complexity is a lifelong goal of mine. About me: I am a practicing antenna engineer, with a PhD in antennas and I have worked for many years in defense, university and the consumer electronics field as an antenna engineer.
Other Projects: A simple physics site entitled Why is the sky blue?You'll not find in these pages the "bible" of EH, but just a simple description of my tests regarding this antenna; I just want to share my test and result with other hams: nothing more.
The Hart EH Antenna consists of two 2 elements having a natural capacity between them. Think of a fat dipole When a voltage is applied to a capacitor an E field will be developed. Also, the current through the capacitor called displacement current will develop an H field at right angles to encircle the electric field. However, when current flows through a capacitor, the phase of the current leads the phase of the applied voltage.
Therefore, the phase of the H field leads the phase of the E field and the difference in phase time prevents satisfaction of the Poynting Theorem for this configuration.
If the external power applied to the EH antenna is first applied to an inductor between the source and the antenna, the inductor will retard the phase of the current relative to the applied voltage.
Therefore, within the antenna the phase of the voltage E Field and the phase of the current which causes the H Field can be made to be the same.
In other words, they occur simultaneously, thus, the name of the EH Antenna. This allows satisfaction of the Poynting Theorem and radiation occurs at the frequency where the reactance of the external inductance causes the phase of the current thru the capacitor to be the same as the applied voltage.
This is at a frequency approximately equal to the resonant frequency of the external L and the internal C of the antenna. Greater amounts of radiation also result from more complex networks.Myth 4
This is due to the very strong fields. The EH Antenna can be physically configured to allow antenna pattern gain in the E plane in two different ways. One enhancement method is similar to that of a microwave horn, even though the operating frequency is such that the physical size of the antenna is very small compared to the operating wavelength.
This is most evident in the Bi-cone version of the EH Antenna, where radiation occurs between and in a very small area at the apex of the cones, and the remaining cone area enhances the gain by shaping the antenna radiation pattern.
The other method is to have long cylinders relative to the diameter of the antenna for the dipole configuration. Due to the necessity of the H field being a closed loop circlethe bi-cone must be non-directional in the H plane. In fact, all basic EH Antennas are non-directional in the plane orthagonal to the E field. Directive gain in the H plane may be achieved with phased arrays made of active EH Antennas, or special shapes. Since the E and H fields are contained, the EH Antenna can not be used as a parasitic element in an array.
Since the antenna is not a resonant structure, the frequency of operation is totally dependent on the external-phasing network. Since the typical phasing network only covers a small range of frequencies, the EH Antenna virtually eliminates harmonic radiation. Since antennas are reciprocal, the EH Antenna offers full performance for both transmitting and receiving. In addition, since the E and H fields are primarily contained within the physical sphere of the antenna, the antenna rejects external E or H fields and receives only radiation.
Thus, the EH Antenna is exceptionally quiet, thus producing very high signal to noise ratios in the presence of man made and atmospheric E field or H field noise.Homebrew EH antenna for 40M band
So, if what people say about EH antenna is true, this very small antenna will perform as good as a full size dipole 80 mt in mt band The following pages are just a short technical describtion of EH I've built; at the end you'll find my test and results. Intro Prototype 1 Prototype 2 Test Results. Prototype 1. Prototype 2.How to Construct a very small but efficient Antenna with PVC Plumbing tube and discarded fruit cans Just the thing to fit in a small space such as the house attic.
There has been some revolutionary thinking on how Electromagnet Waves can be generated. One outcome of that thinking in small efficient antennas is the tubular dipole which has been named the EH antenna. Here we describe a typical antenna assemblies made up for 20 and 40 metres.
However not everybody has access to the Internet and I will give a very short precis of how Ted introduces his subject. It is some years since Heinrich Hertz discovered that radio waves were periodic.
For the last century our concept of the basic antenna has been a resonant half wave with other antennas being subsets of the basic Hertzian antenna. Also about years ago John Henry Poynton discovered the components of radiation which are in brief:. To enable radiation, the E and H fields must be developed which satisfy these requirements. We learn that the E field in a resonant Herzian half wave antenna is developed from the ends of the antenna where the voltage is greatest and the H field is developed essentially in the centre where the current is greatest.
So perhaps there is a better way! We have gone along with the basic Herzian antenna for a century. As a result, Professor Hately, together with several associates, introduced and in fact patented various forms of the Crossed Field Antenna which were designed to generate the E and H fields at right angles, in phase and in the same and comparatively small space.
Ted eventually became involved with documentation for the X Field antenna and went on to develop what he has called and patented the EH antenna. So, I had a go at assembling versions of this antenna, one each for 20 and 40 metres. The article is about how I assembled them and how they performed. The antenna consists of two tubular or conical plates with natural capacity between them. You might consider them to be a fat dipole or fat bi-cone. The E field is generated by voltage across the plates and the H field by the displacement current in the dielectric between the two elements.
The fields intersecting at right angles are shown in Figure 1.
Steve formed the dipole by wrapping sheets of copper around PVC plumbing tube. For my antenna, I selected plumbing tube which nicely fitted around recycled metal fruit containers which I had saved. So my tubular elements are on the inside of the tube instead of the outside. An external matching network is required to transformation from 50 ohms unbalanced line to the balanced input of the dipole with ohms radiation resistance.
A balanced form of L network is used with two inductors and two capacitors. It is an easy matter to calculate the value of these components as each must have a reactance equal to the square root of 50 x RL which equals ohms.
Adjustment of the network apparently also ensures that the displacement current is in phase with the voltage across the plates so that the E and H fields are in phase. From my experiments, the phase correction is that small that it is difficult to notice the deviation from the calculated values I have just quoted.
At this point I must draw attention to the fact that in Australia our standard measurement units are metric. However all the data I have referenced is in imperial units. To avoid any confusion, both to myself and others reading this article in conjunction with the web site, I have purposely kept to the imperial system.
The circuit diagram for my two units is shown in figure 2. I first assembled the 40 metre unit as shown in figure 3. For each cylinder half dipole I used two of our standard Australian fruit containers fruit tins or fruit cans which are 4 inches in diameter and 4. The inside diameter of the PVC pipe I obtained was just a little over 4 inches, so the cans fitted in nicely.Marketing plan conclusion and recommendations
The cans were secured by self tapping screws which also doubled as connecting terminals where required.
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