John wrote: b) The antenna will convert a portion of the applied AC voltage and current into heat energy as a result of resistive losses in the antenna structure.
Unless steel or nichrome wire is used, or electrically poor connections exist in the antenna structure, losses due to (b) will be low. --------------------- That's not correct John, and it's the Achilles heel in all small antennas. We simply do not have conductors that will handle RF with anything like the efficiency they will handle DC or low frequency AC. That's because all the RF current 'crowds' onto the very surface of a conductor. As we make an antenna physically smaller, the impedance drops. As the impedance drops, the RF currents and resistive losses go up. Even silver or gold - the best electrical conductors known - are not nearly good enough for the sorts of currents we see in small antennas. As an antenna is made shorter the resistive losses far exceed any other losses in the system. Of course those resistive losses occur in the matching network too. It's not just the antenna itself that converts RF into heat better than it makes electromagnetic waves. Resistive losses are also the primary source of losses in coaxial feed lines working at high SWRs, for example. If we had better conductors, we'd not care about running 100 feet of 50 ohm coax at high SWR. Even with excellent conductors, we know that coax used that way may consume virtually all of the RF and convert it into heat. To get around those losses we need a room-temperature RF "superconductor", and one hasn't been invented yet. As much as we might like, Maxwell was right. His laws still stand. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
