If paralleled dipoles for different bands on a single feed line are called a "fan dipole" it's a misnomer that can cause a lot of confusion. Sometimes folks pick up short-hand term by accident, like assuming that a dipole is always fed at the center to be a "dipole" when, in fact, a dipole is a half-wave radiator and, being exactly 1/2 wave long it has an electrostatic pole at each end, hence it is a "dipole". It's "dipole-ness" has nothing to do with where or how it's fed RF.
A "fan dipole" is a single-band affair. It's is a way of broadening the bandwidth of a single-band dipole by simulating a "fat" wire using multiple wires. Typically the wires join at an apex at the center and spread or "fan" out at the far end with cross-wires connecting the ends. That forms larger effective radiator diameter that reduces the "Q" of the antenna; hence the bandwidth is increased. It's not a commonly-used antenna because a simple wire dipole usually has adequate bandwidth on 40 meters and up, and in practice even a large "fan" doesn't broaden the bandwidth all that much; not enough to cover the 3.5 - 4 MHz range with a low SWR, for example. However, like any "fat radiator" dipole, the resonant length is shortened a bit, which can be a help in limited space. Cebik has a good write-up on fan dipoles and their close cousin, the bow tie antenna, at www.cebik.com as part of his discussion of small beams. 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
