End fed half wave – NEC models for 20m

Introduction

End Fed Half Wave antennas are again very fashionable with hams, accompanied by extraordinary claims and somewhat sparse understanding (the way of modern ham radio).

To add some light I have created a set of NEC 4.2 models of a half wave antenna on 20m to give some insight into the behaviour of a bottom fed vertical half wave over real ground.

This analysis does not consider harmonic operation, antennas are a half wave at 14.2MHz.

Four models are used:

  1. 20mHW-VEP – bottom fed vertical above perfect ground;
  2. 20mHW-VEA – bottom fed vertical above real ground;
  3. 20mHW-VCA – centre fed vertical above real ground (ie ground independent feed);
  4. 20mHW-HCA – centre fed horizontal at 5m height above ground;

NEC 4.2 model description:

  • 14.2MHz;
  • no conductor loss;
  • real ground assumed to have conductivity=0.005S, ╬Ár=13, of course results are dependent on these values;
  • conductors are ~10m long, 20mm diameter;
  • bottom fed vertical half wave uses a 10m x 20mm vertical driven ground electrode;
  • centre fed vertical is raised 200mm above ground;
  • feed line and feed line common mode current are excluded;
  • the centre of all antennas is ~5m above ground (real or perfect).

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Above are the patterns from the models for discussion. Continue reading End fed half wave – NEC models for 20m