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Re: [TowerTalk] Feedpoint Impedance

To: "Towertalk Reflector" <>
Subject: Re: [TowerTalk] Feedpoint Impedance
From: "Ward Silver" <>
Reply-to: Ward Silver <>
Date: Tue, 29 Jul 2008 08:06:07 -0700
List-post: <">>
>>> Radiation resistance should be fixed..
>> Oh, right...duh.
>> The current equation will do - but the radiator (I may have confused 
>> things by referring to it as a "dipole") may be anywhere between one-half 
>> and one wavelength long, so the current won't be a simple cosine 
>> function.  It *will* be zero at the ends :-)
> I think Orfanidis's book has the equation you're looking for.. actually 
> several approximations, of varying fidelity..
> I'm pretty sure there's some standard assumptions of the current 
> distribution shape (ranging from uniform for very short, to triangular to 
> sinusoidal to something else), possibly broken up into segments.
> What sort of accuracy are you looking for?

20% ought to do it.  There will be significant variation depending on 
proximity of ground, type of ground, and so forth.  At this point, I'm just 
doing a feasibility study.

73, Ward N0AX 


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