How do go/no-go thresholds for SEW link operation get determined?

• A. Based on distance and line-of-sight; thresholds are fixed for the mission.
• B. Determined solely by the transmitter power available, with no other factors.
• C. Set by the regulatory spectral mask without considering mission needs.
• D. Based on required BER/SNR, reliability targets, interference level, thermal noise and system margin; thresholds adapt to mission criticality.

Answer: (D)

The go/no-go thresholds are set by whether the link can meet the required data quality under real operating conditions. It’s not enough to know how far apart the stations are or that the line of sight exists—you have to know if the received signal is strong enough relative to noise and interference to achieve the needed performance.

To decide this, you start with the target data quality, usually expressed as BER or a target SNR for the chosen modulation and coding. From that, you derive the minimum SNR the system must have at the receiver. Then you work through the link budget: transmitter power, path loss, antenna gains, and the receiver’s sensitivity. But the environment adds more: interference from other sources, thermal noise in the receiver, and any additional noise in the channel. You also include a system margin to cover uncertainties like fading, alignment variations, or weather effects. Finally, you adjust the threshold based on how critical the mission is—the higher the priority, the larger the margin and the stricter the BER/SNR targets you enforce.

That’s why this option is the best: it captures the quantitative performance requirements (BER/SNR), the impact of interference and noise, and the adaptive margin tied to mission criticality. The other ideas are too simplistic: distance or line-of-sight alone don’t account for channel conditions; transmitter power by itself ignores noise and interference; and regulatory spectral constraints set limits on use but don’t determine whether the link meets reliability needs in a given mission.