Is there an easy way to detect the phase of a sinusoid that has been added to other sinudoids of different frequencies (through a frequency-division scheme) without using a superheterodyne receiver accurate enough to reject all other signals? All sinusoids in the system have the same amplitude, and their frequencies and phases (other than phase of sinusoid in question) are precisely known. I was thinking that we can use a wide-band filter, and as long as I know the behaviour of the filter precisely (how much of the neighboring signals it admits, etc.), I can post-process the output of the filter in some way.
The system is currently set up so that the multiplexed signal passes through a filter, and then a phase difference detector (AD8302) compares the filter output's phase with a reference signal appropriate to that frequency.
EDIT: It's good to hear back! To clarify, the goal of the system is to detect the change in phase difference. The target sinusoid will change its phase with respect to the reference phase (very slowly) over time due to some chemical process. We would like to monitor this phase change. The absolute phase between the target sinusoid and the reference is irrelevant to us, and so is the filter phase response (since it equally applies to the signal before and after phase change). All components are analog, and the high frequencies of the sinusoid is currently preventing me from sampling the multiplexed signal and from using DSP techniques directly on the multiplexed signal.