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.
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