So, what is balance modulator?

The first disadvantage of standard AM, wasted carrier power, can be eliminated by suppressing or removing the carrier before transmission. This is accomplished by using a balanced modulator. This device mixes the audio RF carrier. Then due to its circuit configuration, it allows only the mixing products or sidebands to pass to the output. The resultant signal is called double sideband-suppressed carrier. It can be transmitted and received without a carrier and received without a carrier and thus offers more efficient transmission than standard AM.

Question: What are the disadvantages of DSBSC.?

First, DSBSC stands for Double Side Band Suppress Carrier.

- In DSB-SC since carrier is suppressed, hence power consumption is reduced and nominal.

- The power in the modulated signal is contained in all four sidebands

- The bandwidth of the DSB-SC signal is doubled that of the message signal.

- Envelope detection not possible.


Other operations

a. Twin FET

Here, the RF carrier input is applied in phase to the gates of Q1 and Q2. This causes equal but opposite drain currents to flow in the primary of T2. The result is zero output when the carrier alone is applied to the circuit. Potentiometer R1 is used to compensate for differences in the two FETs. The output is monitored and R1 is adjusted for minimum or zero output with the carrier only applied to the circuit.

When audio is present, it is applied to the gate of Q1 180° out of phase with the gate of Q2 due to the coupling transformer T1. This sets up a push-pull type circuit for the audio. It also causes nonlinear mixing or modulation across the FETs. The end result is that the mixing products or sidebands are in push-pull across the primary of T2 and, therefore, pass to the output. However, the carrier is cancelled across the primary and, thus, does not appear at the output. The original audio is filtered out by the RF transformer and resonant tank. Thus, the output is a double sideband, suppressed carrier signal.

The amount of carrier suppression depends on how closely the FETs match and also the other components in the system. As mentioned before, R. can be adjusted to improve the balance. Also, the center tap on the primary of T2 can be adjusted for optimum operation. When properly constructed and adjusted, this circuit can suppress the carrier to -60 dB below the sideband amplitude.

b. Diode ring

- Ring modulators frequency mix or heterodyne two waveforms, and output the sum and difference of the frequencies present in each waveform. This process of ring modulation produces a signal rich in partials, suitable for producing bell-like or otherwise metallic sounds. As well, neither the carrier nor the incoming signal are prominent in the outputs, and ideally, not at all.

Two oscillators, whose frequencies were harmonically related and ring modulated against each other, produce sounds that still adhere to the harmonic partials of the notes, but contain a very different spectral make up.

If the same signal is sent to both inputs of a ring modulator, the resultant harmonic spectrum is the original frequency domain. Regarded as multiplication, this operation amounts to squaring. However, some distortion occurs due to the forward voltage drop of the diodes.


Conclusion

Suppressing carrier during transmission will increased the power in the intelligence signal since the carrier which is draining is now suppressed or not present anymore. Thus a cleaner and lesser noise signal is produced.