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Old March 25th 04, 01:59 AM
George
 
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Default EZNEX Modeling Question

Has anyone here modeled physically shortened (i.e. - helix wound) VHF
antenna elements using EZNEC? I'm looking for suggestions how to do this.

George
K6GW




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Old April 2nd 04, 10:50 PM
noexqs
 
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I've modelled a 8 element VHF loop-yagi by describing it into an excel
spreadsheet. I suppose you could do the same for helix type of antenna.
Except that you use an additional Z-axis. I'm not very familiar
with this particular antenna but modelling it shouldn't be so hard.

Therefore, this is what I did with my loop-yagi:
I divided the circumpherence of a loop into 24 parts (of 15 degrees).
Described end-points (x,y) = r*cos(a), r*sin(a) (r-radius, a-angle)
Added a Z value for each subsequent loop.
Modelled into the desired format and exported the output to a datafile
and then imported the results into the modelling software.

After optimizing in the modelling software, I exported the
calculated results and used another
spreadsheet to recover the actual length of the loops, simply by
adding the lenght of the 24 parts of each loop (using basic math).
After verification in a few modelling programs I
then built a prototype 70cm/435Mhz loop-yagi with plain electric
"house-wire"
to validate the calculations. The modelling proved quite accurate.

The endresult now is a 8 element 144Mhz loop-yagi (2WL boom) which gives
about 12.4dBd gain, about 22dB F/B and good pattern for DX
and SAT-work. Another advantage that this antenna
has a very robust construction and by making the radiating
element to rotate, you only need one-and-the-same antenna, no special
feeds for whatever polarisation. This gives amazing results!

Hope this helps.
Suc6 with the job.
Willem, PE2WDO






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Has anyone here modeled physically shortened (i.e. - helix wound) VHF
antenna elements using EZNEC? I'm looking for suggestions how to do this.

George
K6GW







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