Topband: EWE/Flag/K9AY modeling

[Terry Conboy]

At 12:39 PM 2005-07-27, Tod - K0TO wrote:
>Anyone on the list have an EZNEC model of any of these they feel is put
>together correctly. I am uncomfortable with the ones I have done and their
>results. If you are willing to send a model for me to inspect it will have
>to be done off the list since attachments are not permitted.

I'll forwarded some of the EZNEC models I've used to Tod.

The Flag is very easy to model, since no ground connection is 
involved.  The Pennant version is a bit more difficult, since the 
feedpoint is between the wires that connect at a small acute angle, 
which can be a sensitive spot for NEC2.  Dealing with non-ideal 
matching transformers is a concern in actual installations 
(interwinding capacitance, etc.).

The EWE and K9AY both involve connection to ground, which isn't 
allowed with high accuracy ground in the standard NEC2 version of 
EZNEC.  This can be approximated by using 2 or more 1/4 wl radials 
0.001 wl above ground at right angles to the antenna wire.  In fact, 
W7EL includes a K9AY model with EZNEC (not sure which version it came with).

I've found that the K9AY is the hardest to model.  Even small changes 
can make a big difference in the null structure.  It makes it 
difficult to know what is "real".  I think that the actual antenna is 
similarly "jiggery-pokery", leading to the common use of vactrols for 
variable terminations.

Good luck,
Terry N6RY