Ian White wrote:

For a serious earth mat that would put many broadcasters to
shame, see: http://nidxa.org/memberWWW/k9dx_antennas.htm
There's about 40km of wire under there. I book-marked that page to
remind myself occasionally that maybe 1km isn't so hard after
all...

http://nidxa.org/memberWWW/k9dx_home.htm
Blimey, wouldn't it be easier to just phone them?