loud and clear; receiving well
Used in radio communication to confirm that a transmission is being received clearly. Also used figuratively to mean that a message or signal is understood perfectly.
"Roger, coming through loud and clear."
The reply came back over the radio: 'Receiving you loud and clear.'
了解 is a general acknowledgment ('roger', 'understood'), while 感度良好 specifically confirms good reception quality.
Compound of 感度 (sensitivity, reception) and 良好 (good, favorable). A set phrase from radio communication.