Compare superheterodyne and direct-conversion (zero-IF) receivers with respect to image frequency, DC offset, and 1/f noise issues.

• A. Superhet uses IF with image frequency; DC offset and I/Q imbalance are less severe; zero-IF has no IF but suffers from DC offset and 1/f noise.
• B. Direct-conversion uses IF.
• C. Superhet has no image frequency.
• D. Zero-IF has an IF.

Answer: (A)

The key idea is how the downconversion path affects interference and low-frequency noise. In a superheterodyne receiver, the RF signal is mixed with a local oscillator to produce an intermediate frequency. Because a separate RF signal at the image frequency can also produce that same IF, you get an image frequency problem that must be blocked with preselection or image-reject filtering. Once the signal is at IF, you can apply selective filtering at a non-zero frequency, which helps protect the wanted signal from nearby channels.

DC offset and 1/f (flicker) noise are less troublesome in the superhet because the actual demodulation occurs away from DC. The signal doesn’t sit right at baseband during the most noise-rich part of the chain, and LO leakage doesn’t fold directly into the baseband in the same way it does when you downconvert directly to zero frequency.

In direct-conversion (zero-IF), there’s no intermediate frequency, so the signal lands at baseband immediately. That means any LO leakage and self-mixing produce a DC component in the received signal, and flicker noise near DC becomes prominent. I/Q imbalance also shows up as distortions right at baseband, since you’re working essentially at DC.

So the statement that a superhet uses an IF with image frequency concerns, while DC offset and I/Q imbalance are less severe, and that a zero-IF receiver has no IF but suffers from DC offset and 1/f noise, aligns with how these two architectures behave. The other options contradict fundamental aspects (direct-conversion is not defined by an IF, a superhet does have an image frequency issue, and zero-IF does not have an IF).