[RFI] Clamp on RF meter

[Jim Brown]

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