BFO
Wodrick is correct...
If the radio transmitter were a simple AM broadcast transmitter, you would not need the Beat Freq Oscillator.
For example, there is a guy on the microphone with a high-pitched voice (underpants too tight) saying Dit-Dit-Dah-Dit (morse code)...then, you would be able to receive the message without a BFO.
But, if the transmitter were a simple morse code transmitter...like the Titanic sending a morse message for help...you'd need a BFO to receive. (In this case, the transmitter only transmits when sending a morse character. In the case of an AM broadcast transmitter, the transmitter is transmitting all the time...even when the guy talking is pausing for a breath.
By the way, when you receive SSB (single-side-band) on your HF, your receiver has a BFO operating. Without the BFO, you would be unable to receive side band. (This is because SSB is one side band [half of what you have with an AM signal] and has 'surpressed carrier'...which is close to a morse transmitter, in that, between words, the transmitter is transmitting a low-power signal. They do this for better effectivity...it concentrates the transmitter energy more into the words spoken...and doesn't waste the energy on a carrier...or both side bands.)
PantLoad