[Lowfer] antenna current

[John Andrews]

Just a comment that is usually made at this point in a discussion about LF
ground systems:

AM broadcast ground systems are largely based on work done by George Brown
for RCA in the mid-30s. The experimental part was done at 3 MHz. The concept
of 120 wire,  0.25 - 0.5 wavelength long, was based on three goals:
1. To return as much ground current in a low resistance path as economically
possible.
2. Using radials longer than 0.25 wavelength, to provide a highly conductive
reflection point to aid in properly forming the vertical pattern of 0.5 to
0.625 wavelength towers. This is an aid in minimizing fading at the fringe
of the coverage area.
3. To reduce dielectric losses in the immediate vicinity of the antenna.

Of the three goals, only one can be reasonably achieved in back yards at LF,
that is to reduce the dielectric losses close to the antenna. The ground
system is simply not long enough to provide a low impedance return for much
of the antenna current.

So the usual idea is to concentrate on forming a ground SCREEN. Things like
chicken wire are very effective at this, if you can keep it all bonded
together. An elevated counterpoise can be very good, though ugly. Otherwise,
keep the conductors near the surface of the ground if at all possible.

John Andrews