Topband: "return" current - what is it?

Tom W8JI w8ji at
Sat Aug 4 17:48:11 PDT 2012

> Yes current on each side of the feedpoint is always the same but you
> can't see that with an NEC measurement because you are always measuring
> one segment away from the feedpoint and when the current distribution in
> the wires are not equal, there will always be a difference.  Using many
> segments will cause the difference to be small but never zero (unless
> the current distribution on each side of the antenna is symmetrical).
> This is the information Bob was missing.

I think you may be selecting the wrong type of source, if you are using 

In the source-type selection, chose "SI", not "I".   A split source places 
the source at a segment junction, so you can see current leaving each 
terminal of the source.

Maybe Bob was selecting the wrong source type, too. Or not enough segments?

If you do want to use a source in the middle of a segment, which isn't as 
good for this exercise, then use the maximum odd number of segments. On a 
one wire 160 dipole of #16 that's about 475 segments. In that case the error 
is about .001 amperes out of 1 amp, but a split current source is the better 
thing for look at current leaving each terminal. :-)

73 Tom 

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