Balanced-modulator

  
When the carrier level is adequate to switch the cross-coupled pair of differential amplifiers, the modu· lation signal, which has been applied to the gate, will be switched at the carrier rate, between the collector loads. When switching occurs, it will result in the modulation being multiplied by a symmetrical switching function. If the modulation gate remains in the linear region, only the first harmonic will be present. To balance the MC1445 modulator, equal gain must be achieved in the two separate channels.
Balanced-modulator - schematic

To remain in the linear region, the modulation input must be restricted to approximately 200 m V pk-pk. Because the gate bias point is sensitive to the amount of carrier suppression, a high-resolution, 10-tum potentiometer should be used.




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