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Re: [TowerTalk] 80/40 coax trap dipole design

To: Dan Zimmerman N3OX <>
Subject: Re: [TowerTalk] 80/40 coax trap dipole design
From: jimlux <>
Date: Fri, 17 Dec 2010 08:00:13 -0800
List-post: <">>
Dan Zimmerman N3OX wrote:
>> Sure, a parallel LC circuit (trap) will do it but not a coil alone
> Not true.
> An EZNEC model shows that a 110ft dipole 30 feet above ground* resonates at
> 3.64MHz and 7.13MHz when 39uH coils are added 11 feet from each end.   The
> 2:1 SWR bandwidths are narrow (100kHz on 80 and 150kHz on 40) even with
> realistic inductors (Q=100). There is no possibility of stray capacitance
> because in the simulation they're mathematically idealized objects.
Actually, there is some stray C in your NEC model, because even a thin 
wire has capacitance  (around 10 pF/meter, as I recall..)

BTW, Medhurst's paper is online at princeton,80_47.pdf

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