Explanation: The squelch control circuit mutes the receiver's audio output until an incoming signal's strength exceeds a preset level. For maximum *practical* sensitivity, the goal is to hear the weakest possible signals without being constantly barraged by receiver background noise. Setting the squelch "just below the point where the noise breaks through" (C) achieves this balance. By lowering the squelch threshold to the absolute minimum necessary to silence the inherent receiver noise, the radio is poised to open and pass audio for any signal that is even slightly stronger than that noise floor. This allows the operator to hear the weakest available transmissions. Maximum clockwise rotation (A) typically sets the squelch threshold to its highest point, requiring a very strong signal to open the audio. This drastically *reduces* the receiver's effective sensitivity to weak signals. Maximum counterclockwise rotation (B) generally opens the squelch completely, allowing all receiver noise to be heard. While this means no signals are missed due to squelch action, the constant noise is not a proper or comfortable operating adjustment. Finally, the squelch absolutely affects the *effective* sensitivity (D) for the operator by determining which signals are audible.