This article is a tutorial on using an NEC to model a small transmitting loop in proximity of ground.

NEC-4.2 model parameters:

- single turn;
- 1m loop diameter;
- 20mm OD conductor;
- loop centre 1.5m above ground;
- ‘average’ ground (0.005,13);
- 20 segments in loop;
- conductor loss modelled as 0.0033Ω per segment;
- tuning capacitance 197pF with Q=1000 (ie 0.112Ω series R).

Note that NEC-2 is more restricted in the size of segments for good results, and this same problem will require fewer / longer segments in NEC-2, and give slightly different results.

The model tuning capacitance and frequency were adjusted to resonate at about 7.1MHz.

Above is a VSWR plot of the matched main loop, half power bandwidth (ie between VSWR=2.6 or ReturnLoss=6.99dB points) is 12.5kHz, and we can calculate Q=7106/12.5=568.5.

A model run at 7.106 gives us several interesting metrics.

Gain is 9.77dB, and as expected maximum gain is at the zenith. Continue reading Loss components in an NEC model of a Small Transmitting Loop