Indicate which of the following circuits could not demodulate SSB:

Solution(By Examveda Team)

Definition of SSB (Single Sideband) Modulation:
SSB modulation is a form of amplitude modulation (AM) where only one of the sidebands (either the upper or lower) is transmitted, and the carrier is either suppressed or reduced to a very low level. This technique is used to save bandwidth and reduce power consumption. The demodulation of SSB signals requires extracting the modulated signal from one of the sidebands, which can be a complex process.

Option A: Balance modulator
A balance modulator is used to generate SSB signals by suppressing the carrier and one of the sidebands, making it suitable for SSB modulation. It works by mixing the signal with a local oscillator and then filtering out the unwanted frequencies. Balance modulators are capable of demodulating SSB signals, so this option is correct for SSB demodulation.

Option B: Product modulator
A product modulator operates by multiplying two signals (the carrier and the modulating signal), which can produce both upper and lower sidebands in AM. When used with proper filtering, a product modulator can demodulate SSB signals, as it can recover the modulating signal from the sideband. Therefore, this option is also correct for SSB demodulation.

Option C: BFO (Beat Frequency Oscillator)
A Beat Frequency Oscillator (BFO) is commonly used in SSB demodulation to reinsert a local carrier to the received SSB signal. By mixing the received signal with the BFO, the carrier is effectively reintroduced, allowing for the extraction of the original modulating signal. BFOs are specifically used in the demodulation of SSB signals, making this option correct as well.

Option D: Phase discriminator
A phase discriminator is typically used for demodulating phase-modulated (PM) or frequency-modulated (FM) signals. It works by detecting changes in the phase of the received signal. A phase discriminator is not designed to demodulate SSB signals, as SSB requires a different approach for signal recovery. Therefore, this option is incorrect for SSB demodulation.

Conclusion:
The phase discriminator (Option D) is the only circuit among the options that cannot demodulate SSB signals, as it is designed for phase modulation and frequency modulation, not for extracting sideband-modulated information in SSB.