Dear baby_1
Hi
As i understood , your problem is how to detect an FSK signal , right ?
So , if yes , it is simple . as you probably know , FSK , is pretty similar with FM , but with this difference that the message signal is coded , and it is , just a pulse , so , if you use the usual ways that we will use for FM detection , the message signal that will given , will be an square wave ! ( coded signal ) so , you'll need a decoder , ( according to the coder ) , to change it to an analog signal , and then you should amplify it and ........ .
Best Wishes
Goldsmith