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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, εr=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).

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