This is primarily a planning matter. The booklet published by my Department is intended as a guide to MMDS for the general public. The references to tower heights in the booklet are generalisations rather than specifications. My Department expects most MMDS operators to maximise coverage from their transmitters by siting them as high as possible.
The technical conditions to which MMDS operators must adhere do not specify a minimum height. Transmitter antenna heights are limited to those heights necessary to give adequate coverage of the area within range of the transmitter. Operators are also required to adhere to guidelines laid down by the international non-ionising radiation committee of the International Radiation Protection Association — IRPA — on the limits to exposure to radio frequency magnetic fields in the frequency range 100 kilohertz to 300 gigahertz. A tower height of 21 metres would not necessarily conflict with the requirements to observe IRPA guidelines.