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I read in sci.electronics.design that Reg Edwards
wrote (in et.com) about 'Measuring radiation resistance', on Mon, 8 Dec 2003: If the wire end-to-end resistance of a 40m, 14-gauge dipole is, say, 2.76 ohms then - Aerial efficiency = 100 * 140 / ( 140 + 2.76 ) = 98.0 percent. Which is very good, isn't it? It's equivalent to 1/68th of an S-unit which cannot be detected even by using a magnifying glass and the bloody needle stands still for long enough. Which also serves to illustrate how VERY uncrtical are aerial impedance measurements. Reg, The OP is working with very non-ideal antennas, for which the radiation resistance is probably only an ohm or two, and he wants to know if it's 0.5 ohms or 5 ohms, for obvious reasons. I don't suppose there is any realistic way of measuring it, and modelling may be extremely difficult if the antenna shape is not simple. I've seen antenna evaluation does on 1:10 and 1:20 scale models, but we don't know what frequencies the OP is using, so even that may not be practicable, but if it is, one could work back from field strength measurements to radiation resistance, with a big pad between the transmitter and the antenna to 'soak up' the mismatch. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! |
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