I thought it interesting to compare EMR calc with NEC-4 on my lossless octagonal loop (top tuned), 1m across on 40m in free space radiating 1W.

(ARPANSA 2002) RPS3 and AS/NZS 2772.2 require consideration of E and H separately, and the limit for E is 32V/m and H is 0.104A/m at 7MHz for time averaged fields.

Above is EMR Calc results for an antenna with 1.75dBi, approximately that of a lossless small loop. It calculates the safe distance (lower right) at 0.2m.

NEC-4 suggests that the E field at 0.2m above the top of the loop is 720V/m, almost 30 times the RPS3 E field limit, and that the safe distance at 1W is 1.15m above the top of the loop. The H field at 0.2m above the top of the loop is 5.2A/m, over 50 times the RPS3 H field limit and more than double the RPS3 instantaneous H field limit, and that the safe distance at 1W is 1.45m above the top of the loop. So the safe distance above the loop is actually 1.45m, not 0.2m.

Above is a point source calculation at 0.2m from a 1W source using Friis’ formula, the pink distance field warns that such calculations aren’t valid at such close distance except for a true point source, and it reconciles with EMR Calc. It suggests that is how EMR Calc works, and that EMR Calc’s method is not a valid method and its answer wrong.

It is notable that WIA and ACMA support EMR Calc.

## References

ARPANSA. 2002. ARPANSA Radiation Protection Standard (RPS3 2002) – Maximum exposure levels to radiofrequency fields – 3kHz to 300GHz (assuming plane wave conditions).