[Antennaware] Converting I and SI sources to Voltage Sources for NEC-2

[Pete Smith]

I'm a layman non-engineer who needs to be able to convert I and Split-I 
sources to voltage sources so that they will run properly in NEC-2.

For example, a simplified 8-wire yagi model with the source in the 
center  of wire 5 is specified as follows:

GW 9701  1 0.0000  9701  9701 0.0001  9701  9701  0.00001 [this 9th wire 
added to the model]
...
EX 0 9701  1  0 0.0  1.0
...
NT 9701  1  5  29  0 0 0 1 0 0

When run in NEC-2 in this form, the source impedance is wildly wrong and 
the pattern, while the same shape, is somewhat different in magnitude from 
the original  12.7 dBi forward gain vs 12.27.

Can anyone suggest a reference where I can look up and learn a 
straightforward procedure for converting back to a voltage source?  Or, as 
I fear, is the conversion NOT straightforward at all?

Thanks,

Pete Smith