Mobile coverage investigation with my new smartphone.

[CambridgeWorks]

My reason for this investigation is that around 3/4 mile from home is a large supermarket, plus post office. Often frequented. Consistently get "emergency calls only" message on 3 different phones, despite being supposedly good coverage predictions.
Around here, it is pretty flat. I guess less than a metre between highest and lowest points, with just 2 storey houses in between.
Rob