What is work Encoder and modulator for TV Earth station ?

This is a fairly obvious homework assignment. Also, this belongs in the Electronics forum.

However, that said, your question does not really apply to home electronics.

My suggestion is that you do your homework, then send in the answer you derive and see if anyone would be willing to assist you. Some of our Electrical Engineers would more than likely take a look at your work.

None that I know of will just answer the question for you because you learn nothing by having the answer handed to you!