Towertalk
[Top] [All Lists]

Re: [TowerTalk] Funniest thing I've seen in weeks

 To: , Re: [TowerTalk] Funniest thing I've seen in weeks "Jim Lux" Wed, 30 Jun 2004 19:55:55 -0700
 ```While most of the NEETS documents are fine, as far as explaining what's going on, quite simply, the explanation in the referenced link is incorrect. For example: "When the parasitic element is placed so that it radiates away from the driven element, the element is a director. When the parasitic element is placed so that it radiates toward the driven element, the parasitic element is a reflector. " An individual element radiates the same whether it is in an array or not, that is, it has the usual dipole pattern (or one quite similar to it, depending on its length). The magnetic field surrounding a current carrying conductor is symmetric around the conductor. This principle (which can be derived at some length from first principles) is what things like method of moments programs are based on, and for that matter, most of modern antenna design. The overall pattern of the antenna is the superposition of the contributions of all the elements, just summed up (in fact, you can treat a long element as a series of much shorter segments strung together, which is what the MoM programs do) There is almost NO way that an element can be made to radiate preferentially in one direction. (the exception would be where the current distribution is nonuniform around the conductor, thus violating the "thin wire approximation") Again: "The parasitic element is effectively a tuned circuit coupled to the driven element, much as the two windings of a transformer are coupled together. The radiated energy from the driven element causes a voltage to be developed in the parasitic element, which, in turn, sets up a magnetic field. This magnetic field extends over to the driven element, which then has a voltage induced in it. The magnitude and phase of the induced voltage depend on the length of the parasitic element and the spacing between the elements. In actual practice the length and spacing are arranged so that the phase and magnitude of the induced voltage cause a unidirectional, horizontal-radiation pattern and an increase in gain. " I don't know that I'd describe two coupled pieces of a radiator as two coupled tuned circuits. The transformer analogy is more correct, especially with respect to the idea of the magnetic flux from one element coupling to another. As a practical matter, voltages do not result in magnetic fields, currents do. The magnetic field from the driven element induces a voltage in the parasitic element, which then results in a current (since the element is, after all a conductor), which in turn creates another magnetic field, etc. In modern usage, the interactions between the elements are described as a matrix of mutual impedances (or admittances). ----- Original Message ----- From: "Keith Dutson" To: Sent: Wednesday, June 30, 2004 4:50 PM Subject: RE: [TowerTalk] Funniest thing I've seen in weeks > In the following link, read the section titled Operation. > > http://www.tpub.com/neets/book10/42l.htm > > Keith > > _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] Funniest thing I've seen in weeks, W0UN -- John Brosnahan Re: [TowerTalk] Funniest thing I've seen in weeks, Al Williams Re: [TowerTalk] Funniest thing I've seen in weeks, Jim Lux Message not availableRE: [TowerTalk] Funniest thing I've seen in weeks, Jim Lux Re: [TowerTalk] Funniest thing I've seen in weeks, Tom Rauch Re: [TowerTalk] Funniest thing I've seen in weeks, Jim Lux RE: [TowerTalk] Funniest thing I've seen in weeks, Keith Dutson RE: [TowerTalk] Funniest thing I've seen in weeks, Jim Lux RE: [TowerTalk] Funniest thing I've seen in weeks, Keith Dutson Re: [TowerTalk] Funniest thing I've seen in weeks, Jim Lux <= RE: [TowerTalk] Funniest thing I've seen in weeks, Keith Dutson NEETS text inaccuracies Re: [TowerTalk] Funniest thing I've seen inweeks, Jim Lux Re: [TowerTalk] Funniest thing I've seen in weeks, GALE STEWARD Re: [TowerTalk] Funniest thing I've seen in weeks, Robert Shohet RE: [TowerTalk] Funniest thing I've seen in weeks, Keith Dutson RE: [TowerTalk] Funniest thing I've seen in weeks, Jim Chaggaris