Length calculation of shorted (TRX) feeder wire

 Dear hamoperator, for the generally consideration of reaktance for a shorted feeder wire is following formula generally applicable:    

Zr = Zo * tan(360 * l/Lambda) for degrease or   Zr = Zo * tan(2*pi * l/Lambda) for radianten calculation

Wether degrease or radiant calculation you must switch it on your pocket calculator.  Zr is the reactance from the load, Zo the input impedance of the wire, l the length or wire an lambda the wave length (300/frequency in mc)  

Now a special case - resonance length:

For lambda/4 and uneven more of that takes effect:  Zo² = Za * Ze    ====>  parallel resonance circuit

Zo is the wire impedance, Za the output load (also Zr reactance matching) and Ze the impedance of input load.  

For Lambda/2 and even more takes effect:                Ze = Za             ====>  serial resonance circuit


Wire length               Frequency                Cable impedanc

m     mc     Ohm     Solution:       Ohm          Positive solution: the feeder will be capacitive on the antenna otherwise inductive

 Here you can view the charts for the most cable impedances an frequencies! 




Arthur     DL7AHW



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