CATbox is a modular computer aided transceiver (CAT) interface system comprising four standalone matrix board cards. One, or at most two, of these cards can be contained in a Hammondbox – the CATbox. A MAX233 chip and a regulated power supply are common to all the cards. The MAX233 chip solves the problem of converting from the rig’s TTL computer interface voltages to those of the RS232 connection on the computer.