The distance of one sixth lambda comes from empirical data taken from a
Hertzian dipole antenna. In his book Introduction to Electromagnetic
Compatibility ISBN 0-471-54927-4, Clayton Paul writes: The point where the
1/r3 (cubed) and 1/r2 (squared) terms become insignificant compared with the
Here is the actual text:
(2) At frequencies below 30 MHz,
measurements may be performed at a
distance closer than that specified in
the regulations; however, an attempt
should be made to avoid making measurements
in the near field. Pending the
development of an appropriate measurement
procedure
Hello group.
I substantially agree with the comments of Allen Tudor
Don Umbdenstock. My own view is :
I believe the 40 dB / decade (of distance) is a questionable approximation
for extrapolating the measurement antenna location being reduced from 10
meter to 3 or possibly 1 meter in an
The difference is the transition region.
Simplified expression of transition region is lambda/2pi. At some number of
wavelengths above this point the propagation roll-off is linear, i.e., 20
dB/decade. Well below 30 MHz, near field phenomena are encountered. Also,
antenna configurations may
Sounds to me as if they're being doubly cautious here. First they warn you
not to make measurements in the near field. Then they use the 40dB per decade
extrapolation factor to account for measurements taken in the near field (or
perhaps the cross-over point between the near and far
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