Which letter indicates that the phone is sound powered?

The correct indication that a phone is sound powered is represented by the letter J. In telecommunications, particularly in maritime and aviation contexts, specific letters are assigned to denote the power source of different communication devices.

When identifying a sound-powered phone, the designation is important because it informs operators about the method of powering that device. Sound-powered phones operate without any external electrical supply, utilizing the sound of the person's voice and the inherent design of the phone to transmit and receive audio signals. This feature is particularly valuable in environments where electrical systems might be compromised.

Understanding these designations can help maintenance personnel quickly recognize equipment capabilities and ensure it is appropriately utilized in operations. The other letters correspond to different types of power sources or functionalities, but J is specifically used for sound-powered phones.