I read on pg5 of Antenna Simulation with 4NEC2 about shortening factor "x". It is very specific and I can't figure out how to use it in a general nec file. It sounds like SY x=0.907 in the nec file will shorten all the Y parameters, but that doesn't make sense to this newbee. I would think it would reduce the larger dimension (end) to yield the 0.907 reduction. Maybe it does. I tried it on my file with no apparent result. IE, the plots did not change to reflect a different resonant frequency. Anyplace I can find a better explanation of this feature? thanks
The answer to your question is on page 6 of Antenna simulations with 4NEC2 including an application example for 2300MHz:
A symbol (SY), x, is defined as having the value 0.907. This value is used in the calculations for the lengths of the dipole arms in the following GW statement.
I prefer doing this with the Symbols tab in 4NEC2's "NEC Editor (new)" (see Settings). The defined symbols are used in entries on the Geometry tab to define wire endpoints and other values.