++++++++++++++++++++ See also Antenna EH +++++++++++++++++++ From: "Stuart Rohre" To: "John, KI6WX" , "Elecraft Mailing List" Subject: Re: [Elecraft] E-H Antenna Simulation in NEC Date: Mon, 3 Mar 2003 11:31:50 -0600 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 +++++++++++++++++++ From: "Stuart Rohre" To: "Tony Wells" , "John, KI6WX" , "Elecraft Mailing List" Subject: Re: [Elecraft] E-H Antenna Simulation in NEC Date: Mon, 3 Mar 2003 11:45:53 -0600 Tony, the FLEX antenna will probably offer you all the compactness you desire and still decent bandwidth, (70 kHz at 7 MHz), all in a size that is no more than 8 feet tall at 160m, and proportionately smaller at higher bands. Now these are one band antennas at this time, but our R&D group is working on multiband models. We have working models of 60 per cent efficiency only 6 inches high for 20m. If you go up to 14 inches high you can get up in the 90 per cent ranges for total efficiency. And this is the antenna alone radiating over a ground plane 6 by 6 feet, not the feedline radiation, as a balun is used or a cable choke. Papers have appeared in Antennas and Propagation of IEEE USA, and in IEEE Antennas Symposium proceedings, June 2002. The secret is a folded unipole element, which is replicated a total of four elements in parallel around a cone shape. The feedpoint is the point of the cone, the wide end has the shorted side of the quarter wave lines that make up elements. The angle of the cone support is typically 40 degrees. This for the 14 inch slant height model. The inventor is Robert Rogers, a local K5. Applications to date have been for ship to ship communications and ship to shore, as well as ocean research buoy telemetry to ship or shore. These are all HF ground wave and sky wave experiments, but the ground wave is much better than the typically helical short vertical on fiberglass rod. 73, Stuart K5KVH ++++++++++++++++++++ Date: Mon, 03 Mar 2003 18:51:09 -0800 From: "John, KI6WX" Subject: Re: [Elecraft] E-H Antenna Simulation in NEC To: Elecraft Mailing List Stuart; The nice thing about NEC is that it allows you to calculate things that you can't easily measure. The antenna cylinders are 98% efficient, but the matching network described in the patent will lose over 99% of the energy passing through it when connected to a 0.03 ohm load. The overall efficiency of the antenna is less than 1%. -John > 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. > ++++++++++++++++++++++ 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 +++++++++++++++++++++