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

Subject: Re: [TowerTalk] 80/40 coax trap dipole design
From: Ian White GM3SEK <>
Reply-to: Ian White GM3SEK <>
Date: Fri, 17 Dec 2010 13:27:09 +0000
List-post: <">>
DJ7WW wrote:
>Barry's designs use a loading coil in each leg rather than a trap, and
>the coils are roughly at the point where the insulator would be for a
>half wave on the higher band. Then the coils, and a bit more wire.  The
>160/80 version is roughly 160 ft long, the 80/40 version is a bit under
>100 ft.

>It will not work on two bands without a trap

Yes, it will. The point you are missing is that the mode of resonance 
changes between the two bands.

On the lower band, the mode of resonance is a conventional shortened 
half-wave; the current has the same phase along the whole length of the 
wire. But on the higher band, the coil creates a different "1.5 
wavelength" resonance mode which includes a phase reversal.

The change of mode is what makes the dual resonance possible.


73 from Ian GM3SEK

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