Telex 38109-977 manual

and switching systems much earlier, and now it would be applied to matrix intercom systems.

In a TDM matrix, the incoming signals from users (microphones or headsets) are run through an A/D converter and assigned a “time slot” on a TDM backplane. A good (although not strictly accurate) analogy would be the signals on a cable TV system. Whereas on the cable system you might have ESPN, HBO, and MTV, on a TDM backplane you would have the timeslots for Director, Producer, and Camera1. A user can then listen (or be talked to by) any or all of the timeslots. Determining which signal is heard is under software control, and can (generally) be selected by the listener, or pre- programmed. It can also be a function in which other users are calling the listener at that moment.

Figure 4.5 An example of how multiple signals are “time-sliced” for use in a TDM system.

Again, if you use the cable TV analogy, it is easy to understand why the systems do not have to obey the square law. In a conventional square law matrix, adding a single user to a 100-user matrix requires the addition of 201 crosspoints (1012-1002). In the TDM world, it requires the addition of two simple bits – a “transmitter” for the already existent time slot, and a receiver to tune in the other time slots for that user to hear.

C h a p t e r 4 - I n t r o d u c t i o n t o M a t r i x I n t e r c o m S y s t e m s 51