++++++++++++++++++ See also Antenna EH Antenna EH2 ++++++++++++++++++ Date: Tue, 04 Mar 2003 02:15:44 -0800 From: "John, KI6WX" Subject: Re: [Elecraft] E-H Antenna Simulation in NEC To: elecraft at mailman.qth.net Trev; The NEC software is based on a solution of Maxwell's Equations. For wire types of structures, it solves Maxwell's Equations using the Electric Field Integral Equation. For surface types of structures, it solves them using the Magnetic Field Integral Equation. The program is capable of solving complicated structures. Its accuracy and limitations are well documented in the scientific literature, and it can easily solve a fairly simple antenna structure such as described in the EH Antenna patent. So the real question is does the EH Antenna embody a new method of electromagnetic radiation that violates Maxwell's Equations? I would place my money on Maxwell's Equations since they have survived for more than a century and are still considered a exact solution for electromagnetic radiation. The EH Antenna is a conventional antenna fed by a matching network. The patent states "The phasing and matching network aligns the relative phase between the current and the voltage of the radio frequency power signal so that the H-field component of the corresponding electromagnetic signal is nominally in time phase with the E-field component". This is exactly what happens in every antenna and is called the Poynting vector. If the E and H fields are not in time alignment, the antenna will not radiate. I can't tell you what is happening to the power feeding your antenna. However, it is going to one or more of the following places: - Radiation from the antenna - Power dissipation in the antenna - Power dissipation in the matching network - Radiation from the coax - Power dissipation in the coax - Power dissipation in the transmitter (most people don't realize that transmitters can dissipate power that is not radiated by the antenna) You will need to do a carefully controlled set of experiments to determine where the power is going in your setup. -John KI6WX > Forgive me for asking this, its a serious question. Does the EHs > 'claimed' method of operation not make the use of NEC as a model > useless? Surely NEC algorithms are based upon conventional antenna > theory?. > > Also, If the EH matching arrangement is that poor, where does the power > go? My home-made EH does not even get warm and neither does the 4 foot > of coax feeding it. > > Trev G3ZYY ++++++++++++++++++ Date: Tue, 04 Mar 2003 05:40:09 -0500 To: "Stuart Rohre" , "John, KI6WX" From: Charles Greene Cc: elecraft at mailman.qth.net Subject: [Elecraft] Modelling an EH Antenna Stuart and John, I have done some modelling of my 20 M EH antenna in EZNEC as a short, fat dipole, with the physical elements of the EH antenna including the network and coax, and got results. The network was at the antenna just like the real EH antenna and the coax a .5" wire to the antenna mast base. I plugged this network into the KM5KG Network program and assuming a Q for the coils and caps got the losses in the network, which were low. So for kicks, I modelled the antenna without the matching network and got the R J components of the antenna, which showed a very low R and very high -J, as to be expected. Then I used the KM5KG program to model a L network to tune the antenna with these r J components and plugged this network in my short, fat dipole model in EZNEC instead of the EH network at the same point; i.e., at the antenna. I had to tweek the L and C values quite a bit in EZNEC (which may be a modelling artifact) to get the short, fat dipole to load, but got a 50 +0 impedance. The losses in the L network modelled in the KM5KG program were low too. Not what I expected, but if valid, indicates a way to load a short, fat dipole without the loss with a L only loading network. Prior communications with Roy Lewallen indicated that a reasonably short dipole can have a decent gain, but the problem is in the R losses in the loading network and the antenna itself. I don't know of any way to measure or model the losses in the antenna elements themselves in a short, fat dipole and they may be high, but if there is a way to get the losses in the matching network down, that is a step in the right direction. This shouldn't be a surprise for anyone, as L networks have been around for a long time. I just wonder why they haven't been used more in the antenna itself. I would be interested in exchanging model files for EZNEC and continuing this discussion for the sake of advancing out understanding of what is going on. You wrote: "John, a clarification please, certainly the efficiency of the large cylinders is large, taken as themselves alone, right? That is the 98 per cent efficiency you quote? Because of the losses in the matching network, (practical network which surely would have a Q of far less than 1000, ) you then see the overall antenna efficiency as only 1 per cent, correct? IE the antenna has to be taken as a system and the inefficiency of the matching detracts from possible efficiency of the whole. The standard method of measuring small antennas is a Wheeler cap, a closed cylinder that can be placed over a test antenna above a ground plane. Measurements of Z of the antenna with and without the cap can be entered into calculations to produce efficiency based on the low radiation resistance component of Z, and the high loss resistances of the antenna system. We have such a Wheeler cap at work, and are measuring locally produced FLEX antennas. I hope to use the cap after hours someday to measure an EH for which I collected parts. Thanks for doing the modeling, it is very informative. Very low radiation resistance is a big hurdle, but even dummy loads radiate some. 73, Stuart K5KVH" 73, Chas, W1CG K2 #462 ++++++++++++++++++++ Date: Tue, 4 Mar 2003 10:59:47 +0000 To: elecraft at mailman.qth.net From: Trevor Day Reply-To: Trev at secornwall.com Subject: Re: [Elecraft] E-H Antenna Simulation in NEC Thank you for your considered (and swift) reply John. I suppose I really ought to try and find the time to catch up with the theory. I will let you know if and when I find out where my RF is going :-) Trev G3ZYY (must get back to work; its fortunate I work from home) ++++++++++++++++++++ From: "Stuart Rohre" To: , "elecraft" Subject: Re: [Elecraft] E-H Antenna Simulation in NEC Date: Tue, 4 Mar 2003 14:26:35 -0600 Trev, There is only one set of laws for Physics, you cannot invoke an exception for any one Antenna! No, there is nothing in the claimed operation of the EH that should not respond to the same method of moments calculations as the simple dipole or any other antenna, for antenna modeling breaks ANY antenna into miniscule parts looking at the effects of current upon tiny sections then adding all those up to get the overall effects. If an antenna fails by that standard, it is not converting current to radiation as efficiently as standard antennas. (Those existing for many years). The EH antenna attempts to corrupt the well known Maxwell's Equations and consider only the E field separately from H field, while it has been known and can be demonstrated that an E field always produces an H field and vice versa, and they interact together to produce the radiating wave. There is no free lunch, if you do not provide sufficient structure of low losses, and the appropriate discontinuity, (see "Antennas" 2nd Ed. by Kraus), to launch a certain wavelength, the efficiency of that launch is compromised. The structure must be sufficient to overcome the losses of any matching network used to transfer the energy to the antenna. As to where does the heat go in your EH, there are a number of places. Mismatch losses in the feeder may be allowing less current in the antenna than you assume. Have you inserted an RF ammeter between the rig and a dipole, and the rig and the EH for comparison? Most ham signals are not key down for long periods which would introduce noticeable heating, ie low duty cycle. Heat starts to build up and then dissipates in metal structure of the antenna, to air, and feedline braid along its length, into the dielectric of the feeder, etc. Have you looked at the sample with a thermometer that can detect small rises in temperature of the materials? "Working" of an antenna can be done with a small percentage efficiency, but a fraction of the total source power. The signals would be so much better if the antenna did perform at top efficiency. Using superconductors for the matching network would enhance the possibilities of the EH. But, in open air, all antennas have to exhibit the Physics upon which modeling is based, and used not only for antennas performance, but Moments are used to analyzer performance of airframes, cars, roads, bridges and any system appropriate to dissection into its basic parts. 73, Stuart K5KVH +++++++++++++++++ From: "Stuart Rohre" To: "John, KI6WX" , "Charles Greene" Cc: Subject: Re: [Elecraft] Modelling an EH Antenna Date: Tue, 4 Mar 2003 18:28:41 -0600 Sounds good, John and Charles, The modeling with L network is intuitively what I would expect. You have reduced L and its attendant losses, by substituting the less L with a C which should have inherently lower losses. L networks are great and forgotten by hams. The modeling of small dipoles should be in past issues of "Antennas and Propagation" of IEEE, which college of engineering libraries often carry back issues of. We are doing similar work with our Folded Conical Helical antennas developed by Dr. Robert Rogers, an on going project here. Similar concerns to the EH, and other antennas such as the Bilal Isotron. Some of the small antennas work also parallels work Sevick did on short verticals some years ago in QST etc. 73, Stuart K5KVH ++++++++++++++++++