Carrier Signal - RF (Carrier)
A carrier is a pure sine wave of constant frequency that carries no information on its own; information is imposed on it by varying the amplitude, frequency or phase of that wave. The value referred to when a remote control is said to "work at 433 MHz" is the centre frequency of this carrier. The receiver separates the signal from the others by tuning to exactly this frequency.
Radiating the information directly is not practical: button data is low-frequency and radiating it would require antennas kilometres long. Instead, the data is used to vary one property of a high-frequency carrier.
- If the amplitude is varied you get ASK/OOK.
- If the frequency is varied you get FSK/GFSK.
- If the phase is varied you get the PSK family.
The carrier has two practical consequences. First, the receiver looks only at a narrow window; transmissions outside the window are largely suppressed, and this is the basis on which many devices can operate on the same site. Second, the stability of the carrier frequency matters: if crystal tolerance and temperature drift shift the carrier out of the receiver's window, the link range drops or the link is not established at all. In frequency-hopping systems the carrier does not stay fixed but moves within the band in a defined pattern; AXI's XRF protocol uses this architecture.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety
Do not confuse: what is described here is the radio frequency carrier onto which information is imposed. For the PWM carrier in a motor driver, see the entry Carrier Signal (PWM Carrier).