"JC" wrote
Thanks for help, I think I wrongly explained my problem, here is the
question:
1/ I design an antenna, for instance a 3 el 20m beam.
2/ I enter into EZNEC wires dimensions, spacing, height, source.....
3/ EZNEC calculates gain, F/B, SWR....and results are acceptable.
4/ Now let's suppose my objectives are max F/B as I have a QRM
source
opposed to my favourite transmitting direction and SWR 1.5 on a
given
frequency range as my transceiver is very SWR sensitive and I can't
use an
antenna tuner.
I accept changing wire lengths and spacing but not boom length.
Is there a way to have EZNEC, or another software, doing automatic
iterations until it reaches the best F/B-SWR compromise ?

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Let us see what would be involved if you had EZNEC and had to do
everything else yourself the hard way. You already have a crude,
satisfactory design for 3 elements, wire lengths, wire diameters,
spacing, height, etc.

Only the boom length and presumably wire diameters and height are
fixed and you wish to optimise everything else for maximum F/B ratio
and minimum SWR.

Everything else comprises : 3 lengths and 1 spacing. This makes a
total of 4 independent variables.

You now vary the first variable over a range of say 4 increments,
keeping all the other variables constant and keeping a record of the 4
results of F/B ratio and SWR

You then vary the second variable over a range of 4 increments,
keeping all the other variables constant and keeping a record of the
results.

You continue to do this until you have done all possible combinations
of the 4 variables. You will have a 4-dimension array of results of
F/B ratio and SWR, making a total of 512 observations.

Now search the observations until you can find the maximum of F/B
ratio combined with minimum of SWR

If it looks as though the minimum SWR or the maximum F/B ratio lies
outside the 4-dimensional array then shift the variables in an
appropriate direction and repeat the whole procedure until a max and
min are found.

The trouble with modelling programs is you have to enter element
lengths and spacing via the keyboard. It would be nice to have a
program to do it for you. I am unfamiliar with the situation. Such a
program might exist - one which outputs F/B ratio and SWR.
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Reg.