The idea is that I have a summing amplifier centering the input from my reciever on 0v. This inverts the signal, so I have the inverter to get it the right way round again. The comparator compares the signal to 0v to control a multiplexer, as I only want to know the magnitude of the signal in this bit. So, if the signal is positive, it will go straight through, and if it is negative, there is another inverter, so the resultant output of the multiplexer will be 0v.
I know I could just connect the output of the summing amp to the comparator, but I have tried this and it didnt work either.
I will draw up a full circuit diagram and scan it in on Friday, as it will explain it better.
Thanks for the suggestions so far though.