FT,
There are a few things I would like to clarify. When you refer to the "coverage volume", how are the boundaries of this volume defined for a specific airport/ runway, e.g. are they defined as an angle/ range on the approach charts? I was thinking of the coverage boundary as when the localiser RF signal exceeds a certain threshold.
So to confirm my understanding, basically, the localiser behaves as per ICAO Annex 10 when within the coverage volume. When outside of this volume, at the fringes of where the receiver on the aircraft flags that it has detected a strong enough signal to think it is in coverage, the localiser can be "out of spec", i.e. within +/- full scale and very noisy.
Many thanks for the info everybody.
Cheers,