NEC-LIST: Modeling with NEC

    Can someone give me some assistance with this probelem, please.

    I want to create a NEC81 model of a series fed vertical monopole
and include the stray reactances, i.e., capacity shunting the base
insulator, inductance in series with the lead-in, etc. Assume the
vertical is 1/4 wavelength at 1.5 MHz or 50 meters. It is mounted on
a concrete pier and base insulator combination that is 2 meters high.
It has a two meter lead-in going to a shack sheltering the tuning
network. There is a ground strap running from the tuning network to
the ground system. The whole thing looks like 4 wires something like
this:

                   | 0,0,50
                   |
                   |
                   |
                   |
                   |
-2,0,2 __________| 0,0,2
       (~) |
        | === Insulator Capacity
        | |
        | |
-2,0,0 | | 0,0,0
/////////////////////////////////

    Each of the short wires carries only one segment and the tall
radiator carries 17 making a total of 20 segments. The short wires
are only 2 meters so it is hardly practical to include more segments
on them.
    MININEC places the feed point and the loads at the junction of the
segments. That is where I want the feed point to be. I don't care if
the capacitor is in the center of its segment. On the other hand, NEC
places the feed point and the loads in the center of the segments
unless the feed point is divided into two parts with half the feed on
each of the segments straddling the desired point.
    Now comes the rub!!! NEC instructions say to use parallel
sections of equal length for the straddling sections. That means that
I would have to add at least two more segments on the feed point wire
and since I only have two meters to work with, they will be very
short.
    Is there another way around this?

Thank you very much for your help.

J.L. Smith
jlsmith_at_datasync.com
Received on Mon Jan 26 1998 - 10:14:12 EST