A balanced modulator is a device that modifies a signal, usually in the form of an amplitude modulated (AM) radio signal. It takes the original signal that has both sidebands and a carrier signal, and then modulates it so that only the sideband signals come through the output modulator. This creates a balanced signal, as there is less noise because the carrier signal has been removed.
Amplitude modulation is a way for a signal to be transmitted over distances. The AM signal is originally sent with a carrier signal in the form of a wave, which is then modulated, or changed, by an audio signal that is also in the form of a wave. This produces a signal that has the original carrier signal plus two bands, one on top of the original and one on the bottom. These are referred to as sidebands and are exact copies of each other. A signal like this is called a double-sideband amplitude modulated (DSB-AM) signal.
The sidebands, because they were modified by the originating audio waveform, are the signals responsible for carrying the information that is being transmitted. Once modulated, the carrier signal doesn’t serve a real practical purpose anymore, and it only shows that a signal is being sent. It does, however, take up a larger chunk of power than the two sideband signals, and also creates a less-clear signal.
To remedy, or modulate, this situation, a balanced modulator would be used. This device removes or suppresses the carrier signal, so that only the two sideband signals remain. The signal that remains now has several times more power because the carrier signal is not there to drain it away. This type of signal is referred to as double-sideband suppressed-carrier (DSBSC). In addition to being more powerful, the signal is also “cleaner,” as it has less signal noise, which the carrier signal can often create.
At some point, a DSBSC signal needs to have its carrier signal regenerated to allow for the signal to be put back into its original form for reception. In the case of an AM signal, it allows the signal to be received on the proper frequency and be heard. This can be taken care of by a device such as a beat frequency oscillator.