Sharp FO-D60 Operation Manual page 25

Talking range
The talking range of the cordless handset is approximately 200 m (line of
sight; talking range may decrease depending on transmission conditions). If
you hear noise or interference while talking on the cordless handset, move
closer to the fax machine.
Large metal objects,
metal structures, and
thick walls reduce the
talking range.
Aluminum sash Metal
Setting Up
Reinforced concrete
23