"Bill Turner" wrote -
Performance will be best if it's up in the air, away from ground. RF
does best when flowing through metal, not dirt. Earth is lossy and
should be avoided for transmitting. If you were receiving only, the
loss could be made up by more gain in the receiver, but when power is
lost during transmitting, it's gone forever.

If for some reason you 'had' to mount the vertical at ground level, you
should install enough radials that the antenna does not 'see' the earth
at all, only the radials. To do this, the generally accepted number of
radials is about 120, 1/4 wave long.

===============================

Fine on your comments Bill except for the oft-repeated number of 120 which
must have been originated by Marzipan the Magician. It is far too
extravagant.

For amateur purposes 32 radials are 'enough'. And that only because it's
twice 16, which is twice 8 - - - - down to 2 which is twice 1.

Over a wide range of soil resistivities and radial lengths, the
electrode-to-ground resistance of 32 radials is only about 1.3 times that of
a solid copper disk of the same radius laid flat on the ground.

The electrode-to-ground resistance of 1 radial is about 6 or 7 times that of
32 radials so unless immersed in salt water it may be well worth while
increasing to 4, 8, 16 or even 32.

In average soils and with radial lengths of around 20 metres, the electrode
resistance of 32 radials will already be as low as 3 ohms which is perfectly
good enough for less than a 1/4-wave or 5/8-wave vertical and far better
than necessary for a 1/2-wave vertical. To increase to 120 or more radials
is just a waste of good copper plus a lot of hard labour.

The following table is for a typical ground resistivity = 200 ohm-meters
(conductivity = 5 milli-Siemens), radial length = 66 feet, wire diameter =
14 awg, buried depth = 1 inch.

Radials ohms
--------- -------
1 24.6
2 13.6
4 8.0
8 5.3
16 4.2
32 3.3
64 2.8
128 2.7
Disk 2.5

For a 1/4-wave vertical I wouldn't bother with more than 16 radials with
which efficiency is of the order of 90 percent. Or an undetectable 1/12 of
an S-unit less than perfection.

If ground resistivity is not known, as it nearly always isn't, then a
logical way to proceed is to keep doubling up the number of radials until
the received signal strength of not too distant stable transmissions stops
increasing. Then add 2 or 3 more for luck. But I doubt whether the new magic
number of 32 will be exceeded.

Regarding length of radials. The propagation velocity along wires buried in
the ground is very much smaller than in free space. When lying on the
surface of the ground it about half the free space value. So surface
radials need never be longer than 1/8 wavelengths.

Furthermore, the loss along buried wires is very high. Of the order of 8 dB
per 1/4-wavelength at their own velocity. So there's little point in having
buried wires much longer than 10 meters or 33 feet on the 160m band, and
progressively shorter lengths at higher frequencies. At distances where
there's no current flowing in the wires there's no point in them being
there. Nobody uses ground radials for 15 and 10 meters anyway.

Do I hear anybody shouting "Heretic" ? ;o)
----
Reg, G4FGQ.