Digital Access Carrier System - How Did WB900 Work?

How Did WB900 Work?

Before DACS, WB900 (a 1 + 1 analogue carrier system) was used. The first subscriber's phone (called the 'audio customer') would be connected as normal. The second subscriber (called the 'carrier customer') would have his phone calls modulated on to an RF carrier or Carrier wave on the same physical phone line at around 40 kHz - high enough not to be noticeable to the audio customer.