Topband: 1/2 wave inv L

[Charles Moizeau]

That is probably true but ONLY for an antenna that is 0.25 wavelength high where the current maximum is at the base feedpoint, right where those radials, also the same 0.25 wavelength in their length, connect.


Once the vertical antenna is made longer than 0.25 wavelength, e.g., 0.5 wavelength, its current maximum will no longer be at ground level.  Rather, it will be, and always be, at 0.25 wavelength back from the/an open end.


With the maximum radiation occurring at a higher point, it strikes the ground further away; hence the need for longer radials to gather it in and return it to the feedpoint.


Charles, W2SH




From: Mark K3MSB <mark.k3msb at gmail.com>
Sent: Sunday, February 18, 2018 7:40 PM
To: Charles Moizeau
Cc: Mike Waters; Roger Kennedy; topband at contesting.com
Subject: Re: Topband: 1/2 wave inv L

I've read that the minimum lengths for ground radials is no shorter than the height of the antenna and that 50% of ground losses occur in the first one-quarter wavelength distance from the antenna.

This tells me that "too long" radials have diminishing returns.

I've played the radials on ground game for years;  I think this year I want to try a pair of elevated radials as Mike W0BTU suggests.

73 Mark K3MSB


On Sun, Feb 18, 2018 at 6:56 PM, Charles Moizeau <w2sh at msn.com<mailto:w2sh at msn.com>> wrote:
Well it is understandable.  The current maximum in the half-wave antenna is lifted well above ground level.  Had there been a radial system it would have had to employ very long radials, for most of the vertical's radiation would have been hitting the ground at points far away from the base of the vertical.  It is only at those distant points that very long radial wires would be able to gather the radiation from the ground's surface and feed it back to the feedpoint.


Charles, W2SH


________________________________
From: Topband <topband-bounces at contesting.com<mailto:topband-bounces at contesting.com>> on behalf of Mike Waters <mikewate at gmail.com<mailto:mikewate at gmail.com>>
Sent: Sunday, February 18, 2018 6:31 PM
To: Roger Kennedy
Cc: topband at contesting.com<mailto:topband at contesting.com>
Subject: Re: Topband: 1/2 wave inv L

Yup! The lack of a radial system explains why the 1/2w vertical worked
better. :-)

73, Mike
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On Feb 18, 2018 4:55 PM, "Roger Kennedy" <roger at wessexproductions.co.uk<mailto:roger at wessexproductions.co.uk>>
wrote:


Many years ago, a friend of mine used to operate on 160m with vertical
antennas suspended on a big Weather Balloon filled with hydrogen . . .

After using Quarter-wave verticals for a few months, he changed over to
Half-wave verticals . . . he found they worked much better !

He didn't have much of a radial system (due to lack of space), mainly just
earth rods at the base . . . so I suspect that's one of the reasons why.

Roger G3YRO
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