On 3/29/2011 5:35 PM, Richard Fry wrote:

The current distribution along the aperture of both of these forms of
radiators has a sinusoidal shape. The current at the top of both of
these radiators must be zero. The portion of a sinusoidal waveform at
the operating frequency, beginning with zero current at the top, that
can exist along the aperture of radiators that are physically short in
terms of wavelength, as in my NEC comparison, appears to be a straight
line with zero current at the top and maximum current at the base of the
radiator.

Yes. This is shown in various editions of the ARRL Antenna Handbook and
the ARRL Handbook itself.

With essentially identical current distribution along the aperture of
both radiator forms, it should be expected that the helix and linear
monopoles in this discussion should have essentially identical radiation
resistances and patterns.

This has been shown to be true in the NEC comparison in the OP, and is
supported by the quoted statements from well-respected authors of
antenna engineering textbooks.

Thanks, Richard.

73,
John

John - KD5YI wrote:
On 3/29/2011 5:35 PM, Richard Fry wrote:

The current distribution along the aperture of both of these forms of
radiators has a sinusoidal shape. The current at the top of both of
these radiators must be zero. The portion of a sinusoidal waveform at
the operating frequency, beginning with zero current at the top, that
can exist along the aperture of radiators that are physically short in
terms of wavelength, as in my NEC comparison, appears to be a straight
line with zero current at the top and maximum current at the base of the
radiator.

Yes. This is shown in various editions of the ARRL Antenna Handbook and
the ARRL Handbook itself.

With essentially identical current distribution along the aperture of
both radiator forms, it should be expected that the helix and linear
monopoles in this discussion should have essentially identical radiation
resistances and patterns.

This has been shown to be true in the NEC comparison in the OP, and is
supported by the quoted statements from well-respected authors of
antenna engineering textbooks.

Thanks, Richard.

73,
John


The next step would be to run it plugging in some reasonable number for
the wire resistivity. The patterns should be quite similar. I theorize
that it will show that for same power in at the feedpoint, the "gain"
will be slightly less for the helically loaded one (because there's a
longer wire, so more resistance, for essentially the same current
distribution in the wire).

Then, the question would be whether the helically loaded unit has a
lower loss in a matching network at the base.