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Re: [RFI] Clamp on RF meter

To: rfi@contesting.com
Subject: Re: [RFI] Clamp on RF meter
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Wed, 02 Feb 2011 10:45:34 -0800
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 2/2/2011 10:26 AM, Michael Germino wrote:
> I only used it if I have a problem.  I used it to see where the best 
> placement of the ferrite was.  Sometimes where you think the placement is 
> best, isn't.

Not necessarily. Every wire (or conductor) is an antenna, whether we 
like it or not. A good ferrite choke acts like an open circuit, whereas 
a poor one (not enough turns) acts like an inductor,  and one with too 
many turns can look capacitive. A choke simply ADDS its impedance in 
series with the existing antenna. If it's an optimum choke (near its 
resonance and a high impedance), it acts like an insulator to stop 
current AT THAT POIINT, but if the wire is long enough, the choke might 
turn the remaining wire into a half wave and increase the current in 
that part of the wire. Ditto with the choke that is L or C -- it simply 
shifts the current maxima and minima along that particular antenna.

Bottom line -- measuring (or sensing) current in these conductors is 
certainly a worthwhile thing, but it's easy to mis-interpret the results 
if you don't view what you see in the light of the fundamental concepts 
of antennas.

73, Jim K9YC
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