CWNA starts with RF for a reason: every “Wi‑Fi problem” is eventually a signal, noise, or airtime problem.

dBm without the fog

Received signal strength is reported in dBm. Remember:

• 0 dBm = 1 mW
• Every +3 dB ≈ double the power
• Every −3 dB ≈ half the power
• Every +10 dB ≈ 10× the power

A client at −67 dBm is a common design target for data. Voice/video often wants stronger and cleaner signal than that.

SNR is the real story

A strong RSSI with bad noise is still a bad link. SNR (signal-to-noise ratio) is what decides whether MCS rates stay high.

When troubleshooting:

1. Note RSSI and noise floor
2. Watch retries and data rates
3. Ask whether interference is raising the noise floor

Free space path loss (intuition)

As distance grows, signal drops. You do not need to memorize every formula on day one, but you should know:

• Higher frequency → more path loss for the same distance (5/6 GHz falls off faster than 2.4 GHz)
• Walls, glass, and people add attenuation on top of free space loss

Study prompt

Explain in one paragraph why a client can show “full bars” and still have a terrible experience. Hint: bars often track RSSI, not SNR, retries, or airtime.