"Crazy George" wrote in message
...
Say, for purposes of illustration, that the near field ends at 1
wavelength.
At 2 MHz, that is very roughly 530 feet . At 14 MHz it is about 64 feet.
At 30 MHz, it has shrunk to ~32 feet.

-- Why would the near field end at 1 wavelength? It ends
when the wave front arriving at the receiving antenna becomes planar. ie, to
function efficiently in the far field, the receiving antenna needs to
intercept a planar wavefront. That is, the individual rays need to be
arriving in parallel. If the distance between antennas is very great, that
is very nearly the case.

If the capture area of the receiving antenna is great relative to the
distance to the source, the received energy arrives as non parallel rays
that basically reach the receiving antenna out of phase with each other and
partially cancel. So, the gain of antennas measured in the "near field",
where the received energy is not a planar wavefront, will be in error. The
distance to the end of the near field is highly dependent on the gain of the
antenna and with UHF and SHF antennas often exhibiting very high gain, their
near fields can be and often are very large.

The power collected by a receiving antenna within the transmitters near
field is very nearly constant with distance. In the far field, recovered
power varies inversely with the square of the distance.

Regards

W4ZCB