I think planning depends on height. 8m might be pushing it, most houses are about 6m with a chimney. I guess most TV aerials are <1m, they don't need planning. A quick call to the local council would be best I guess.
Note that the antenna height means the height of both the transmit and the receive antenna i.e. for a link distance of 20km both the transmit and receive antennas must be 22.5mtrs above ground level (at 5.8GHz). The two antennas do not have to be at the same height. As a rough guide, if the transmit antenna is at 16mtrs the receive antenna should be at about 29mtrs giving a total height of 45mtrs.
Or maybe not
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