Topband: Radials on ground v FCP

[Rob Atkinson]

I can't comment on the folded counterpoise because I am not familiar
with it.  The "broadcast model" which I take to mean 120 radials is
used because in the case of a 90 degree tower on medium wave, the
earth current intensity is far enough from the feed point to
necessitate a higher number of radials so that as they diverge, they
are not so far apart from each other that the earth losses are
unacceptable.  Few hams have 1/4 w. towers for 160 m., and instead
employ shorter vertical radiators such as inverted Ls* and Ts, (1/8 w.
for example) so the ground current intensity is high much closer to
the feedpoint.  This means that fewer radials can be used because they
are shorter and at their ends, are still an acceptable separation from
each other.  Of course, ground conductivity plays a part also.  This
is good news for hams who want to save money on expensive wire.  All
of this is detailed in the Griffith book I referenced previously.

73
Rob
K5UJ

*Unlike the T, the horizontal portion of the inverted L radiates.
W1BB recommended extending radials that run along underneath it if
possible, and I think that was good advice.

On Sat, Jan 8, 2022 at 9:27 AM CUTTER DAVID <d.cutter at ntlworld.com> wrote:
>
> Rob
>
> I recall a discussion on here some years ago which proposed that, whilst being an amazing antenna for top band, if you could achieve it, the broadcast model was not necessarily the best use of resources for amateur purposes, on the basis that broadcasters are mainly interested in ground wave to cover a defined relatively short range service area, whereas amateurs a more interested in dx.
>
> I don't recall how that discussion ended, but for purposes of saving wire, at least, the K2AV folded counterpoise (FCP) must be about as good as anyone could attain.  How it performs against that broadcast model would be of interest.
>
> David G3UNA