"Frank's" wrote in
news:ay2_h.21$Vi6.12@edtnps82:

I built the models in 4NEC2 and EZNEC, both using the MININEC ground
feature.

My guess is that the radials are far enough clear of the ground that
NEC- 2 should be adequate for modelling, but it would be interested
to see what results you get from NEC-4.

Re extending wire 10, don't forget it is loaded, so you need to deal
with that.

Owen

Owen, GNEC reports the following. Note I have taken the ratio
of the current magnitudes without regard to the phase relationship.
I can send you a zipped copy of the NEC output file if you are
interested.

Freq TAG 10 TAG 1 Ratio
ABS SEG 169 SEG 1
(MHz) (mA) (mA) (dB)
3.8 1.43 6.5 13
7.1 0.59 5.4 19.2
10.1 0.25 1.0 12
14.1 0.036 3.4 39.5

Large currents in the 3.8 MHz radials are evident
on 30 m. I have removed the loading from TAG 10,
and EK is not required in NEC 4. Also I show
TAG 10 at extending 3 m below ground. Probably
not realistic, but I am always confusing meters with
feet!


Hi Frank,

A plot of this current ratio shows very steep slope around the design
frequencies.

A plot of my model results is at
http://www.vk1od.net/multibandunload...al/new_pa1.gif .

Ratio of mast current to radiator current at junction:

(MHz) NEC-4(dB) NEC-2
3.8 -13 -14.6
7.1 -19.2 -17.6
10.1 -12 -9.9
14.1 -39.5 -38.3

Note that for the NEC-2 model, these were not the optimal frequencies.

Owen