[Antennas] Re: question on short antenna diameters

[Roy Koeppe]

About:

"Antenna is a short center loaded vertical for 40m,
mounted in the clear, consisting of a:

3'x3' base plate with (3) 1/4 wave radials
30" mast/stalk
6"x6" coil
60"-102" stinger

my questions are:
at 7.xx mhz
if the stalk is either 1/2", 3/4", 1", or 1.25" in diameter
will this effect the antenna?
and if so in what ways?"

TIA
-- 
GB de ka5oai,
Sam Morgan

Hi Sam,

No. The diameters you mentioned have little effect on anything. The
ground losses under your antenna, assuming the radials are at ground
level, dominate everything else. Your short antenna has a radiation
resistance of around 5 ohms. The effective ground resistance of three
1/4 wave radials is about 25 ohms. So dividing 5 by 25 and multiplying
by 100 calculates to an over all antenna system efficiency of 20%. Any
concern of conductor diameters pales into insignificance compared to
your other losses. When you run 100 watts into that antenna, only 20
watts is radiated.

73,    Roy    K6XK/0       Iowa