Measuring the bit error rate of TDM telecommunications channels

A device 2 for measuring the bit error rate of a telecommunications channel is mounted on a peripheral PC card and inserted into a card slot of a personal computer 1. The device is responsive to external program commands from the PC. A pseudo random sequence generator 8 generates a pseudo random sequence and sends it through an output means 3 for connection to a time division multiplexed telecommunications link in response to program commands received from the PC. Comparison of the received and transmitted sequences may be performed using an XOR gate and the transmitted sequences may be received either at a second test device or at the originating device via loop back. The sequence may be generated using a predetermined generator polynomial, eg X15 + X14 + X2 + 1.