I am building the same exact same spectrum analyzer but I do not have a 4017 counter in my schematics. Can you tell me what is the purpose of the 4017 counter.

 

Welcome to the forums.

It's better to start your own thread rather than hijacking an old one - http://forum.allaboutcircuits.com/showthread.php?t=32342

Not knowing the extent of your question, the 4017 is a decade counter. Any IC's data sheet can be found by using the chip number in a search engine.