Length calculation of open feeder wire on the transceiver

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

Zr = Zo * cotan(360 * l/Lambda) for degrease or   Zr = Zo * cotan(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    ====>  serial resonance circuit

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

For lambda/2 and even more takes effect:                Ze = Za             ====>   parallel resonance circuit


Wire legth                 Frequency                  Cable impedance

m     Mc     Ohm     Solution:       Ohm          Negative solution: the feeder will be inductive on the antenna otherwise it is capacitve.

Here you can view the charts 


 Arthur     DL7AHW




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