Noise Floor
The noise floor is the baseline energy level measured at the receiver input when no wanted signal is present; it is expressed in dBm. When industrial sources are added on top of thermal noise this floor rises and the receiver's catalogue sensitivity becomes meaningless in practice. This is the quantity that really limits range.
A receiver decodes a signal not by its absolute level but by how far it rises above the noise. As the floor rises the same signal becomes harder to read; range shortens even if you do not change the transmitter power.
- The thermal floor is physical and increases with bandwidth; a narrowband receiver has a lower floor.
- The industrial contribution comes from inverter switching, welding arcs, unfiltered switching supplies and brush arcing.
- Its effect can be calculated: if the floor rises 6 dB the theoretical range halves; if it rises 12 dB it drops to a quarter.
That is why the most common cause of the complaint "the remote control worked at 100 metres yesterday, today it cuts out at 30" is not a device fault but a new noise source that has come into service on site. The right diagnostic method is to switch off suspect equipment one by one and measure the range again. The permanent fix is to suppress the source with shielded motor cable, ferrites and supply line filtering.
Context where this term is used: Wireless remote control installation: pairing, relay, safety