[TowerTalk] Field Strength comparison

[Lux, Jim]

On 9/5/21 12:36 PM, Richard (Rick) Karlquist wrote:
> Instead of using rules of thumb from ancient history, you can get a 
> far more precise answer by simply modeling the antennas under test and 
> the test source on EZNEC.  Should take 10 minutes or less.  If you can't
> go far enough to get into the far field, you will at least know the
> correction factor at the distance you can do.  The modeling results
> also provide a sanity check on your actual measurement. 


An excellent suggestion..

But it's a bit tricky to determine where near field/far field "boundary" 
is - The basic NEC RP will give you "far field"  And you could look at 
near fields separately.

RP is "far field only", even if you give a distance - it just scales the 
field by the distance. But you could do RP with a specified distance. 
ANd then do a NE, NH with the same distance, and compare.

One could "illuminate" the antenna with a type 4 excitation (current 
source) and look at the feedpoint voltage with a 50 ohm termination, and 
then move the current source away until you see a nice 1/r curve.

-

Or, more simply, model a short test dipole with a resistor load at the 
feed, which is a 'e field probe'. Feed your antenna with the excitation 
as usual, and then look at the current through that test resistor, as 
you move the dipole away.