Wire antennas Part 3: Summary. What you need to know.



On any antenna certain things will always be true:


Voltage will be high or highest at an open end.

Current will be zero or near zero at an open end.

Voltage is always high a half wave or any integral multiple of a half wave from an open end.

Current will always be zero or near zero at the end and at an integral multiple of a half wave from an open end.

Low voltage points coincide with high current and vice versa.

The voltage to current ratio is the impedance. 

High voltage points are high impedance points.

High current points are low impedance points. 

Antennas shorter than quarter wave are capacitive. 

Antennas between quarter and half wave are inductive.

For best results, horizontal antennas should be at least a half wave above ground.


Any conductor near an antenna can affect that antenna. Any nearby conductor a half wave long will have a significant effect on the antenna. Worst case is if that conductor is parallel to the antenna. It can act as a parasitic director or reflector. Even a conductor a quarter wave long can have a significant effect. 

 

Always think of lengths and distances in terms of wavelength. What is long on 10 meters is short on 160 meters!


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