Electronic – Determining type of modulation

Your perfectly single-sideband suppressed-carrier modulated sinusoid certainly has a phase which can be measured. However, what you cannot tell is what the contributions of that measured phase from the audio input and the RF oscillator were.

There is another form of single-sideband modulation, in which not only one sideband but also the carrier component is transmitted. This provides a reference which can be used to synchronize the receive LO to the transmit one - normally done to insure exact tuning, but it would also give you the ability to recover the original audio phase.

It is also quite possible, especially with modern DSP gear, to transmit two separate audio channels, one on each side band. This is commonly called independent sideband modulation (ISB).

Many spread spectrum implementations are DSP based and capable of receiving multiple channels at once - GPS being a good example.

As you describe it, with one way communication from a single master to many "slaves", the task is very easy.

The master simply sends messages of the form Address + Data. All slaves hear all messages and each slave checks for message with its own address and actions them while ignoring the rest. As the master has complete control of the transmitting this can make very efficient use of the channel capacity (when efficiency is needed).

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If you want to go the other way and have many "outposts" sending messages to a single central location in response to messages from the Master (usually on a channel of its own) "the fun begins". Out of such a need has risen much of the data comms protocols that we see today, and the internet.

The (or a) classic early initiator was named "Aloha Net" ("Hello Net") operated by the University of Hawaii to outposts around the islands. This used the simple method of an outpost "just sending a message when it had one". If it did not get an acknowledgement within a certain randomly set time it would send it again. This allowed for radio fade and noise and collisions with other messages. This works well when the total message transmit time is a small percentage of the tome available and when message lengths are short compared to time between messages. This would often apply to home automation applications, allowing an easy two way communications protocol when you find you need or want two way commiunications - as you soon will :-).