Hello there,
There is an application or two that i can think of that uses this type of
modulation.
One is a remote transmitter/receiver system that works over ordinary
household power lines (like 120vac 60 Hz) rather than totally wireless.
The carrier signal transmitted has a frequency of 200kHz.
The second is the same really, but digital information is transmitted
for the purpose of controlling lights and other appliances remotely,
by simply plugging in the transmitter to a home ac outlet.
They both work on the same principle...
The transmitter injects a signal onto the power line and the receiver
uses a filter to monitor the 200kHz signal and reject the 60Hz line frequency.
The 200kHz signal would appear to ride on the 60Hz line sine wave.
wizard: check out National Semiconductors site to see if they still have
app note AN146 available online. This is a full writeup of the circuit
i mentioned first.