Topband: "return" current - what is it?

[K4SAV]

Tom W8JI wrote:
> I think you may be selecting the wrong type of source, if you are using
> EZNEC.
>
> 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.
>
>   
I forgot about the SI source.  That will effectively place the source at 
a segment junction.  Actually it places two sources in the middle of two 
adjacent segments and that simulates almost the same thing 
(insignificant difference if you have sufficient segments).  Since the 
currents are listed at the center of segments, the listing will have the 
currents at the ends of the two sources, which of course will be the 
same value you assigned to the source.  Current is not allowed to change 
between those two segments because the currents are forced to be the 
assigned value.

This won't work if you use the dual voltage source (SV), which 
effectively places it on a segment end (with enough segments).  Because 
it is implemented as two voltage sources on adjacent segments, the 
current is allowed to change between the two segments, and you will see 
a difference in current at the ends of the SV source (assuming an 
antenna with unsymmetrical currents in each side).

None of the NEC sources violate Kirchoff's laws, but the implementation 
of the SI and SV sources isn't exact and doesn't exactly approximate a 
real source (for which NEC doesn't allow you to see the actual current 
at the ends of the source).  But why bother, most people know the answer 
anyway.  The problem is just understanding what the numbers mean that 
the program is giving.

Jerry, K4SAV