On 23 mar, 23:55, Richard Fry wrote:
A few years ago there was some discussion on r.r.a.a. about helically-
wound, normal-mode monopoles, and the rather common expectation that
they had higher gain than a linear monopole of the same physical
height (and with other things equal).

A recent NEC-2 analysis of this topic might be of interest:http://i62.photobucket.com/albums/h8..._Linear_Monopo...
.

Also this link to a page from John Kraus' ANTENNAS FOR ALL
APPLICATIONS, 3rd Edition:http://i62.photobucket.com/albums/h8...y-woundVertica...
.

//

Hello Richard,

Maybe there is confusion between gain and directivity.

When there is no change in the phase of the current, and overall
physical length 0.25 lambda, directivity will be 1.76 dBi (or 4.76
dB over perfect electrical conducting ground).

I can imagine that part of the matching can be in the helix (lots of
copper) so that the ohmic loss may be less w.r.t. to a lumped coil at
the feed point. If so, the gain of the helix can be higher.

If you can make the helix electrically longer then 0.25 lambda (so
that current maximum is not in the feed point, but for example in the
middle), directivity will not change, but ground loss will reduce as
the helix will have high Re(Zin).

Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me.