This thread started with a person trying to find an antenna that would work reasonably well that does not take up much space. While in theory, you are correct the practical aspects of making a very small antenna for low frequencies lead to impossible parameters. The radiation resistance of a dipole 2 meters long for 3.8 mHz is about 0.134 ohms. Since placing such an antenna in free space would require the assistance of NASA we need to assume that it is a bit lower. If we assume that the person cannot or does not want to erect a tall mast, probably a height of about 3 meters would be reasonable to expect. This would make for a radiation resistance of about 0.006 ohms and need. The capacitive reactance will require 397 microhenrys to cancel out which in turn will require a coil 4 inches in diameter and about 24 inches long with 160 turns (about 168 feet of wire). Then you would need an 8333/1 balun transformer with its associated wire resistance. Clearly not a very practical way to make an antenna that would radiate straight up and would have a bandwidth less than required for a single sideband signal. Now if you have theoretical inductors and capacitors and no resistance wire available to you, maybe you can do better. (Calculations by EZNEC)
A more practical solution for a ham that cannot afford or is prohibited from putting up a large antenna is a mobile antenna attached to a porch rail or rain gutter or whatever metal that is available. Better is the common trap vertical. If a person has a bit of space and can erect a 30 or 40 foot mast all sort of possibilities present themselves. This has certainly been an interesting thread and can go on forever if we choose. Hams have been designing, trying and debating antenna designs since Marconi started it all and I don't think it will end soon. 73 to all, Cookie, K5EWJ --- John Magliacane <[EMAIL PROTECTED]> wrote: > When it comes to antenna efficiency, it is important > to understand > that when RF energy is applied to any antenna, three > things will > invariably happen: _______________________________________________ Elecraft mailing list Post to: [email protected] 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
