All small (compared to a wavelength) loops have the same pattern
and an infinite-depth null.

Alas, they have separate patterns for electrical and magnetic
fields. A tall loop tends to act as a vertical antenna and pick
up plenty of electric field. So where you have your nice automatic
magnetic field infinite null, it's filled in by electric field
which can't be cancelled by a magnetic field since it's 90 degrees
out of phase (otherwise it would just shift the null).

Shortwave tends to give you electric field responses faster than
MW, just owing to the relative size of the loop and the wave getting
larger as the wave gets smaller.

In addition, as said, multiple or moving apparent sources owing to
ionospheric bounce may make a permanent null difficult to find.

Careful construction is said to reduce the electric field response
to something very small, so you get deep unfilled-in nulls.

An amplifier on the loop amplifies the magnetic field response mostly,
and so gives the same effect as good construction without having to
have good construction.

--
Ron Hardin


On the internet, nobody knows you're a jerk.