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From: Alan
Date: 16 Apr 2003
Time: 04:13:23
Remote Name: 20.138.254.2
Stefano - Thanks for the reply and I am glad the antenna is giving excellent results and many QSOs. The method for estimating efficiency from the bandwidth, that I mentioned, has to use the correct data, and I am not sure you have applied it correctly, because the "lossless bandwidth" has to use the true radiation resistance, and I think that the measured input resistance of 35 ohms might contain some loss resistance as well. This is a probelm for antenna measurements because when you measure the input resistance of the antenna, it's not clear how much is radiation resistance and how much is loss resistance. To solve this problem you have to use an independent estimate of the radiation resistance, and my estimate based on classical theory was 0.08 ohms as I said. Using your measured reactance of 2000 ohms, the lossless bandwidth is therefore 7000kHz * 0.08 / 2000, i.e. 0.28kHz, and this can be compared with the measured bandwidth of 400kHz to give an estimate of the efficiency of about 0.1%. . . . This is only an academic question when the antenna is used for ham radio, because you have made this antenna work successfully, but I am interested in using novel antennas for other applications outside ham radio, and our customers are quite demanding. They require accurate quantitative evidence before they will accept a new product and that is the problem that is faced by the EHA and the CFA at present. The theory is only qualitative, no proper theory has been presented (e.g. a solution for the field distribution), and for that reason nobody wants to invest time and money into practical demonstrations and measurements. . . . A lot of theory still needs to be done on the CFA, for example, and up to now nobody has received a doctorate for studying it - there is still an opportunity there. . . 73s, Alan