The CEA-909 standard calls out two different communications modes, A and B. Mode A is unidirectional, namely tv/convertor box to antenna only. Mode B is bidirectional, where in the smart antenna and tv/convertor box talk to one another. By far mode B is the best way to go… but nothing is ever simple.
The problem is, the standard left the details for mode B ambiguous as to what data is sent back and forth. Each smart antenna operating in mode B has a program identifier, such that the box/tv knows what types of data to send back and forth. As one might expect, as new mode B devices come on the market, unless the tv or converter box has a firmware upgrade, it wont know what data to send. Granted, some of this may be addressed in CEA-909A (being cheap, ie this is a home project, I got the old standard…)
However, all is not lost, if a tv or convertor box doesn’t know what to do with a given program identifier, it defaults into mode A operation… and the standard requires that ALL smart antenna devices must operate in mode A. Its not the optimum of course, but I can put a lot of intelligence in my smart antenna such that with the limited data available from mode A, I should be just fine. Also,being mode A is unidirectional, comms firmware is much simpler.
Mode A provides for the following data:
rf channel number
In many ways, even in the unidirectional mode A, this is pretty powerful. Of course, the question comes to mind as to how intelligent the tv/convertor box is. The standard calls out the capability to automatically set the parameters for optimum signal, or manual, where the user enters the data, or a provision for both methods. Until I get my AVR running, I wont know what my CECB is capable of…. the owners guide left that out, probably for good reason to avoid confusing the average user.