FSK (Frequency Shift Keying)
FSK is modulation in which binary information is carried by shifting the carrier frequency between two distinct values. Because the amplitude stays constant, the receiver bases its decision on frequency rather than amplitude and remains largely immune to amplitude-natured industrial noise. In sub-GHz FSK receivers, typical sensitivity is reported in the range of −125 to −130 dBm.
An FSK receiver measures the difference between two frequencies; even if an arc, a spark or switching supply noise moves the amplitude of the signal, the frequency information survives. In the field this comes back directly as range.
- Frequency deviation: the larger the difference between the two levels, the better the noise margin, but the occupied bandwidth grows.
- Bandwidth: narrowing the receiver filter reduces the noise power and improves sensitivity; the price is a lower data rate.
- Transmitter stage: because the amplitude is constant, the power stage can be run in saturation and efficiency rises.
Since the payload carried in a remote control is a few bytes, narrow band and low data rate are not a loss but a deliberate choice. In practice FSK links go noticeably further than OOK links at the same output power; you see this difference especially in plants with inverters and in workshops where welding is done.
Context where this term is used: 433 MHz or 2.4 GHz?