Feed impedances against various grounds, and losses

[Guy, K2AV]

For the record...

The following table gives the lost power and radiated power for a
terrible ugly lossy 100 ohm ground used as a current sink for various
antenna feed impedances. Using 100 watts to the feedpoint.

Ant    Gnd     Pwr    %     -dB   Typ
Feed   Pwr     to     Eff   gnd   Ant
Z      loss    Ant          loss

30     77w     23w    23   -6.4   1/4 wave vert

50     67w     33w    33   -4.8   extended vert

450    18w     82w    82   -0.9   single wire Windom

1000    9w     91w    91   -0.4   end fed halfwave with no feedline


If you can manage a 50 ohm lossy ground...

30     63w     37w    37%  -4.3 db

50     50w     50w    50%  -3.0 db

450    10w     90w    90%  -0.5 db

1000    5w     95w    95%  -0.2 db



If you can manage a 25 ohm lossy ground...


30     45w     55w    55%   -2.6 db

50     33w     67w    67%   -1.7 db

450     5w     95w    95%   -0.2 db

1000    2w     98w    98%   -0.1 db



>From this you can see that getting the feed Z up to 450 and above
takes even a terrible ground pretty much out of the equation.

73, Guy



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