> Loop/light does show radiation, so although not easy, why
> not use one to determine what's going on overall?
Brett,
A loop in the nearfield does not show radiation. A small
loop in the nearfield almost exclusively shows the magnetic
induction field.
Near any antenna the induction fields are the dominant
fields. Radiation is a weak effect. The reason we work long
distances with radiation is radiation weakens by wave
spreading. It's a volume of surface area the wave occupies
problem. On the other hand the induction fields only affect
charges in an area where the fields between points fringe
out. They decay rapidly outside the nearfield to nothing.
Even though we measure or define the radiation and induction
fields mathematically as "magnetic" and "electric", it's
really just an effect or force on other charges that we can
easily quantify. The root cause and the rate of decay is
totally different when we look at radiation or induction
effects.
When we take a "magnetic" loop or electric flux detection
system into the area of an antenna, the overwhelming forces
on the detector are from uneven charge distribution
(electric field) and charges moving (magnetic field). These
are energy storage fields, not radiating fields. In a high Q
system, like a small resonant antenna, the induction fields
(electric and magnetic) are greatly increased.
An example of this is a grid dip meter. With a very tiny low
power oscillator, the high operating Q of the coil produces
a very strong magnetic field. That magnetic field can easily
be significantly stronger than the magnetic field detected
from radiation in an antenna that allows us to work
thousands of miles.
Consider the very strong local field around a high Q
resonant tank circuit. Even one hundred watts can cause
enough circulating current to heat the thick blade of a
screwdriver red hot (the blade acting like a small diameter
closed loop), yet it can't be heard a mile away.
On the other hand I can run power into an antenna that will
barely light a flashlight bulb into an antenna that can be
heard thousands of miles away.
There are ways to sort out what is doing the radiating, but
it sure isn't by sticking a small loop near various areas of
the system!!
73 Tom
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