Sorry this is way off topic in relation to noise generation at LF/MF but I know of one case (as I was the responsible investigating engineer for a well known .gov dept at the time) of a tree causing non intentional radiation as a result of mixing of 45Mhz TV signals from Old Meldrum and a nearby "lowband" FM transmitter in Aberdeenshire - the resultant non linear (arent they all) mixing process from this Horse Chestnut tree (and it was the only one in the line of fire) caused wobbly FM interference to a "fixed High band service" -
the Tree in question was about 5 miles from the TV transmitter on a ridge and a couple from the VHF transmitter. The interfered with rx source was some 100m from the Chestnut tree - It was confirmed that the interference was coming from the mid section about 5 metres from ground level - a case of the Bark being worse than the byte. Ill leave you to guess how I cleared the problem.
Its the only one and only kind I came across with during my career and I couldnt really believe what the test equipment was showing - but it was - we didnt go interalia the causes and bio-causes of such an effect but it did exist - honest gov.
youll know my respect for the globally dispersed Acacia tree and how marvellous it is as enhancer of LF signals wrt probes - so perhaps the trees speak more than we really think at RF...
Laurence
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