DESIGN OF A 30-CHANNEL PCM TRAENSMISSION SYSTEM.

Twenty-four-channel PCM has now been in widespread use for a decade but recently CCITT discussions have recommended 30-channel working as an international standard. This can make more efficient use, under favorable conditions, of existing de-loaded junction cables. Whereas in the earlier system signalling utilized one bit in each 8-bit channel time slot, in the 30-channel system the signalling and synchronizing informations in two separate channels. This enables full 8-bit audio coding to be used, providing still higher transmission performance. The system described is based on the specific requirements of the British Post Office and in general conforms to the new CCITT recommendations.