Explanation or website for learning about RF and IF stages?

[HandyMan]

Hello everyone. Could someone either supply a good website address (I have tried Googling) or please explain to me the basic functioning of the RF and IF stages in a TV set?

I just want to understand the basic of what happens after the RF signal enters the tuner, what the IF stage does and how the IF stage splits the audio and video, and the job of the sound filter crystals. I thought the IF stage split the audio and video signals and after doing something, they sent the signals on to the appropriate circuitry, but on a schematic I saw, it showed the sound filter crystal being used on the video output to filter out sound carrier wave, yet I thought the audio would have already been removed?

And I know the sound filters use different frequencies for different systems (Pal I, Pal BG, etc.) but since they seem to be used to filter out sound from the video output, what is done differently in the different systems in order to take the sound from the original mixed input signal, since just altering the sound filter alone obviously makes no differene to the audio when converting Pal I to Pal BG, etc.? - There's either an inductor core to turn or in more modern sets, a setting in the menu to change, but what is that doing and how?

Thanks a lot.