What you are probably seeing is the various "corrections" for end effects
and loading. The "resonant length" for a dipole (where resonant is defined
as having zero reactive impedance component at the feedpoint ) depends to
some degree on the surroundings (i.e. the ground properties for a monopole
over a conductive ground) and the length/diameter ratio of the antenna (a/l
in the antenna literature). It also depends on whose analysis you want to
start with King, Hallen, or Schelkunoff (sp?), since they all come up with
slightly different numbers for approximating the feedpoint impedance of a
particular configuration.
Even in a method of moments model, there's the whole issue of how you treat
the end of the conductor. Is it a flat cap? Is it a rounded hemisphere? etc.
----- Original Message -----
From: "Paul B. Peters, VE7AVV" <ve7avv@shaw.ca>
To: "TowerTalk" <towertalk@contesting.com>
Sent: Sunday, November 07, 2004 4:41 PM
Subject: [TowerTalk] Half-Square formula?
Over the past couple of weeks I have been researching the half-square
antenna. While a combination of magazine articles and Internet-based
information produces a significant amount of data and experiences with this
antenna, the one thing that varies is the formula used for both the
horizontal and vertical elements.
For example, on LB Cebik's site http://www.cebik.com/scv4.html he suggests,
"the relatively invariant relationship between the horizontal and vertical
dimensions of the half square for a maximum-gain configuration tends to
assure a good utility for the formulas". Where H is the horizontal length in
feet, V is the vertical height in feet, and f is the frequency in MHz, he
suggests the use of V=278/f MHz and H=447/f MHz.
In other articles, the number for both H and V elements is either 468, 492
or 1005 and the half or quarter wave product of these calculations. Suffice
to say, the base numbers produce some significant swings in the two values.
While I tend to lean towards the LB Cebik material -- simply given the mass
of research he has undertaken over the years, I am curious what the members
of this group can offer in terms of opinions on the formula.
My thanks in advance for any and all replies.
73 de Paul, VE7AVV
StoneyGround Station
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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