VK2MEV wrote:...
Ideally it would be nice to have a visualisation that draws an isosurface of constant H/E field intensity which designates the unsafe volume. OpenDX can do this nicely, it might be worth hacking up something in C so it runs faster but I'll see how Octave goes first; the equations have a lot of complex arithmetic which gets a bit fiddly in C.
An interesting project Geoff.
You might be replicating to a small extent what takes place in NEC.
I use NEC-4 to do a spatial analysis of E and H fields (separately) in the space around an antenna to evaluate compliance with the standard.
Above is a plot of H field at head height in the plane of a G5RV in inverted V configuration at a certain power level, the origin is under the centre of the antenna, so the plot is just one side and just the region around head height, a fuller plot shows it is safer at lower heights... just that 4NEC2 has some graphics bugs on larger plots. It can be seen that the H field max is not at the centre of the antenna, but well towards the end, a result of the current distribution on 20m and the inverted V configuration.
There is a very popular tool used by hams which apparently has ACMA endorsement though I cannot see a clear statement of that, or the methods used within that calculator but its results do not suggest separate analysis of E and H components at lower frequencies that appears necessary under the standard.
That is fortunate for hams as I can't think of any inexpensive tool that discloses its methods and can calculate E and H components separately.
Something you may find interesting is to plot the value of E/H in the space around an antenna, it varies quite widely, converging on 120 pi a long way from the antenna. This is no doubt the motivation for the standard requiring separate analysis at lower frequencies.
Owen
PS: I understand that there is a revision to the ARPANSA standard expected, and that it may set lower exposure limits in some scenarios.
