Any size PMR scheme can be accommodated using an expandable Communications Interface Unit (pictured). This provides control of hilltop site equipment over a landline or microwave link. The CIU connects to the base AVL computer via serial links with robust error corrected protocols. Hilltop site monitoring is also available with warning signals passed to the control staff should there be any problems with a hilltop link.

The mobile data equipment also provides the facility to switch between data and voice communications providing flexibility without the need for two separate mobile radios.