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Re: [TowerTalk] Ferrite Cores in Trapped Dipoles

To: "Dan Zimmerman N3OX" <n3ox@n3ox.net>, towertalk@contesting.com
Subject: Re: [TowerTalk] Ferrite Cores in Trapped Dipoles
From: Jim Lux <jimlux@earthlink.net>
Date: Tue, 06 Feb 2007 16:36:19 -0800
List-post: <mailto:towertalk@contesting.com>
At 04:10 PM 2/6/2007, Dan Zimmerman N3OX wrote:
> > A trap, especially at high power, is not a good place to use any kind
> > of ferrite or powdered iron core. Ferrite is notorious for saturating
> > on current peaks and thereby causing distortion and harmonics.
>
>Yet many of us are using autotuners (which all have powdered iron
>inductors) on pathological matching cases, probably with high
>circulating currents.

I would say it's not so much that ferrites are notorious for 
saturating, it's more like it's easy to screw up a ferrite design so 
that it will saturate. People build multi tens of kW switching power 
supplies with ferrites.  There's a ferrite transformer in the output 
stage of a 10kW RF power amplifier my officemate was building for a 
research project.  All a matter of good design.

The problem is that designing magnetic circuits is not easy, nor 
intuitive, so a casual approach based on copying another design and 
modifying has a high probability of unforeseen effects.  For folks 
who do it on a day to day basis, it's probably easier, but, to me, it 
seems much more a black art than, say, a straightforward triode or 
FET power amplifier design. (but the power converter designer might 
say the reverse.. he thinks designing magnetics is straightforward, 
but wouldn't contemplate taking on a Class AB FET design.)



Jim, W6RMK 


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