Signal, Noise & Coverage

Read the Units First

RSSI is a received-signal measurement, commonly reported in dBm. A value of −50 dBm is stronger than −75 dBm. Noise floor is a separate measurement of the background; a guessed noise value does not produce a measured SNR.

Signal-to-noise ratio is the difference in dB: RSSI − noise floor. A −55 dBm signal and −92 dBm noise floor give 37 dB. Use measurements from the same radio and conditions.

Do Not Turn a Threshold into a Promise

A useful signal target depends on the application, client and design. Voice handsets, a stationary sensor and a laptop transferring files do not necessarily need the same margin. Interference, retries, airtime demand and roaming still matter.

Our calculator deliberately does not label a number “guaranteed good” or convert it into Mbps. Measure the workload at busy times, not just beside the access point.

Placement Before More Equipment

• Place access points in open, useful locations—not buried in a cabinet, behind metal or at the far edge of the area.
• Check both directions: a powerful access point does not give a small client a stronger transmitter.
• Walk the actual work area and compare devices. A single weak client can differ from the rest.
• Use a wired comparison when possible to separate wireless issues from internet or server issues.

Remember the Three Questions

Can it hear? Can it take a turn? Can the rest of the path keep up? These are coverage, airtime and end-to-end capacity. Signal bars answer only part of the first question.