On 10/30/2012 07:56 PM, Bob K6UJ wrote:
I believe with frequency changes of 10KHZ the wire length changes by about one
foot.
So if it is resonant at 1.800 and you trim off one foot it will be resonant at
1.810.
If you can find the resonant freq (where the lowest SWR is) then you can see
how far you have to move.
Usually I use an MFJ antenna analyzer to see what the frequency of
lowest SWR is, then calculate how much to shorten (or lengthen) each
end of the antenna: (234/current frequency) minus (234/desired
frequency). That had worked well until I started putting up several
antennas in close proximity to each other. With the current crop of
antennas that method proved nearly useless, since the frequency of
minimum SWR did not move by the expected amount. My somewhat
uneducated assumption is that when the antenna is significantly
interacting with something in its environment, all bets are off.
73,
Paul N1BUG
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