> According to the field strength graph in N6PL's vertical antenna
> book, 15 1/4 wave radials under a 1/4 wave radiator would yield
> an efficiency ~70% of that which would be acheived using 113
> radials (e.g. - 1.5dB). This data appears (although it doesn't say
> explicity) to correspond to average soil (~5ms/m). The book references
> G.H. Brown's work at RCA as the source of the data.
....and 120 radials are totally useless, unless the radials are about
1/2 wl long. Efficiency effectively stops increasing at about 50
radials when the radials are 1/4 wl long, and efficiency is very high.
It is almost never worth the effort or cost to use 120 radials, even if
they are 1/2 wl long.
The 120 radial myth comes from the FCC, because stations using
120 radials at least 1/4 wl long are considered by the FCC to be
"perfect". The FCC overkilled the number of radials needed, just to
be safe.
73, Tom W8JI
W8JI@contesting.com
|