[Kymmy]

The transponders are on the satellites, each sat has many transponders and each transponder might deal with more than one channel.

The LNB (Low Noise Block Convertor) is a device at the end of the dish that takes the signal from the sat (about 10-11Ghz), amplifies it and then converts it into a lower signal (.09-1.2Ghz) that is then transmitted down the co-ax to the receiver. The LNB also is able to switch between polarizations (for example Horizontal or Vertical depending on the voltage supplied to it)

So in simple terms this is the path a signal takes from for example Sky to your box

Sky Offices >> Groundstation >> Receive transponder on Sat >> Transmit Transponder on Sat >> Your Dish's LNB >> Coax >> Sat Receiver