Coil-Shortened Vertical Antenna Calculator

You can shorten a vertical antenna by using a loading coil. This online calculator tells you how the amout of inductance your loading coil will need to have.


Coil-shortened vertical antenna

Total height of antenna in feet
   

Distance from antenna base to the center of the coil in feet. (Enter "0" for a base loading coil.)
   

Diameter of the conductor in inches
   

Operating frequency in megahertz
   

 


Results

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Use the Coil Inductance Calculator to design your loading coil. (Calculator opens in a separate page.)

Notes

  • An effective system of ground radials is even more important with a shortened antenna.
  • The already low input impedance of a quarter-wave vertical will become even less as you shorten the antenna.
  • Raising the antenna above ground over a counterpoise of elevated ground wires can increase efficiency and input impedance.
  • The size of the required coil increases with height. Placing the coil about halfway up is a good compromise.
  • You can further reduce the height of the antenna by placing a capacitance "hat" at the top.
  • This calculator was adapted from the Coil-Shortened Dipole Antenna Calculator.)
  • If you would rather calculate the length of a full-size vertical antenna, see The Quarter-Wave Vertical Antenna Calculator.

References

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