Topband: Kinstar AM Radio Station Antenna Design

Doug Waller NX4D at
Thu May 25 14:10:50 EDT 2006

>The short answer is "yes."  In fact, just about everybody on this list has either built or used one.  It's called an inverted L.

This answer may be too short.  Build this antenna over a perfect radial field and the short answer may be correct.  But for those making do with less than a perfect radial field, the Kinstar design could offer some improvements.  Don't let the words "Invention" or "Patent" preclude closer consideration of this design.

The first thing I did was to model the Kinstar vs. the "cage" antenna.  Eznec calculated a higher gain for the Kinstar.  Then I added series resistances of 10, then 20 ohms, simulating poor ground.  The Kinstar design then calculated at a fractional dB loss vs. the "cage" antenna's several dB loss.  I concluded that either Eznec was in error, or that the Kinstar design DID offer some advantage.

Wider spaced vertial wires form an RF void inside their circle.  Electric lines of force repel each other to form a circle of force lines outside the verticals.  Lossy ground inside the circle is eliminated.  Even a near perfect wire radial field close to the base of a single vertical is inefficient due to half the fields around the radial wires being in the ground.  This close-in loss, where power concentration is high, can be eliminated or reduced by using solid metal plate in lieu of wire radials, or by a using a Kinstar-fed cage.

The model of a four-wire vertical, forming a 40 foot diameter circle at the base, and sloping together at the top of a 60 foot tower, looks like a winner.  Gain is maximized by using two or four horizontal topload wires.  Any slope, up or down, appears to decrease gain.  I modeled a fat four-wire cage, using only a single coax feed, and the gain dropped to that of a single wire vertical, the only advantage being more bandwidth.

I hope to build a Kinstar this summer, between DX'peditions, and will advise if I find any advantage of an actual working antenna.  In the meantime I hope some of you will experiment with the Kinstar, especially if you are located on a small subdivision lot, like I am.

73, om Doug / NX4D

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