FCC Exam Question: 3-78L4

What is the common method for determining the exact sensitivity specification of a receiver?

A. Measure the recovered audio for 12 dB of SINAD.
B. Measure the recovered audio for 10 dB of quieting.
C. Measure the recovered audio for 10 dB of SINAD.
D. Measure the recovered audio for 25 dB of quieting.
Correct Answer: A

Explanation: Receiver sensitivity is commonly and precisely determined by measuring the input signal level required to achieve a 12 dB SINAD (Signal-to-Noise And Distortion) ratio. SINAD is a critical metric because it quantifies the purity of the recovered audio, comparing the power of the desired signal to the combined power of noise and distortion components. A 12 dB SINAD level is an widely accepted industry standard for specifying the minimum discernible signal (MDS) sensitivity of a receiver. It represents the point where the received signal is clearly intelligible above the background noise and any inherent distortion generated within the receiver, making it a robust and objective measurement for comparing different receivers. While "quieting" methods (like 10 dB or 25 dB quieting) measure the reduction in noise output when a signal is present, they do not account for distortion. Therefore, quieting measurements are less comprehensive and less precise for a complete "exact sensitivity specification" than SINAD, which includes distortion in its calculation. Furthermore, 10 dB SINAD is not the commonly accepted standard threshold; 12 dB SINAD is.

Pass Your FCC Exam!

Study offline, track your progress, and simulate real exams with the GMDSS Trainer app.


Includes Elements 1, 3, 6, 7R, 8, and 9.