[TowerTalk] Flat top vs Inv Vee

[w8ji.tom]

I looked at results in a paper published by Jack Belrose comparing full
blown NEC-2 to actual full pattern measurements by Haagn and Barker over 30
mS/m soil, and the error was about 5 dB at .05 wl height with a dipole. A
review of the Haagn-Barker data shows NEC-2 gives about 5 dB extra gain at
low heights, when compared to the real world. That's a big error!

The model dipole was in close agreement with real measurements above .1 wl 
height, the higher the better.

Your suggestion the very low antenna ends seriously degrades performance is
a good one. My antennas are all over extensive radial systems, and have the
ends well up over 80 feet. My results might not compare well to bare dirt
below with low antenna ends, and apparently the model might be more
unreliable than I suspected as any part of the antenna is brought near
earth. This has been interesting and useful. I'll pay more attention to end
height, and view the model more critically. I should have thought of that,
since my measurements of currents in a Beverage antenna were about 50%
lower than NEC predictions (meaning NEC calculated less loss than really
occurs for a low horizontal wire).

I'd be happy to pay you for a copy of the paper...
 
> The  definitive paper on dipole efficiency over  imperfect earth
> appeared in the November 1972 issue of the IEEE
> Transactions on Antennas and Propagation, p. 766
> with important corrections on p. 755 of the  September 1973 
> issue.    It is entitled "Radiation Efficiency of a Dipole Antenna
> above an Imperfectly Conducting Ground,"  by Peder M. Hansen.
> 
> Maximum efficiency occurs at heights well above one wavelength.

I assume that is for bare earth, sans any extensive wire counterpoise. 
Do they do anything over a counterpoise system? 

73 Tom

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