[Antennas] Re: question on short antenna diameters

[Sam Morgan]

Roy Koeppe wrote:
> 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
> 
snip

 >> 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.
 >>
Well let me add a little more to the mix here,
the 3'x3' plate with the radials attached...
will be placed on a 2nd story flat roof...
does this effect your comments any?


-- 
GB de ka5oai,
Sam Morgan

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