RF Field Guide · reviewed reference
Noise floor and interference
A strong signal is not useful when the receiver's noise and interference leave too little separation for the selected mode.
Question
What should a planner measure before choosing a channel and committed rate?
Inputs
- Receiver noise figure and channel width
- Spectrum observations over time
- Desired and interfering signal levels at each endpoint
Answer
Working
Thermal noise is approximately −174 dBm/Hz at 290 K before receiver noise figure. Add 10 log10(B) for bandwidth and the receiver's noise figure for a starting estimate; real deployments also include external noise and co-channel or adjacent-channel interference.
Visual explanation
- Desired signal
- Noise floor
- Interferers
- SINR
- MCS choice
- Margin
Interpretation
Record spectrum scans at both ends and at the intended channel width. A clean transmitter site does not prove a clean customer-side receiver environment.