What is the advantage of using a balanced crystal mixer?

• A. It increases LO noise
• B. It broadens IF bandwidth
• C. It reduces image frequency
• D. It cancels out most of the local oscillator noise

Answer: (D)

Balanced mixing relies on symmetry to suppress unwanted LO-related signals. In a double‑balanced mixer, the LO drives two switching paths so that the LO signal appears with opposite phase in each path. When the RF is mixed with this LO, the desired product (the RF×LO content) remains, but the LO noise and LO leakage tend to cancel at the output due to that opposite-phase contribution. The result is a cleaner IF signal with much less LO-induced noise, which improves the receiver’s sensitivity and reduces spurious Fields from LO feedthrough. This is why the main advantage is reducing LO noise at the output. The other statements don’t capture this benefit: the IF bandwidth is set by filters and circuit design, not by the balanced nature; and image-frequency concerns are addressed by other design aspects, not primarily by a balanced mixer’s LO noise cancellation.