Valid Signal
The frame accepted by the receiver, that is, a data packet that both carries the correct identity code and passes the integrity check. Active stop and watchdog decisions are taken solely on the basis of these frames; seeing energy on the radio does not by itself mean a valid signal.
Electromagnetic noise of every kind constantly reaches a receiver's antenna. The receiver does not count this raw energy but the frames that pass all three checks:
- Is the frame structure in the expected form, is the synchronisation sequence recognised.
- Does the identity or address code belong to a transmitter taught to this receiver.
- Does the checksum field agree with the calculation.
If any one of the three fails, the frame is invalid; the command is not executed and the watchdog counter is not reset. This is where the importance of the concept lies: active stop is triggered not by the absence of a signal but by the absence of a valid signal. Even if a strong interference source floods the band, the receiver correctly detects that it is receiving no command and stops.
Knowing this distinction in the field speeds up diagnosis: if the remote does not respond, the problem is not always range; a neighbouring noise source may be preventing valid frames from being read.
Context in which this term is used: 433 MHz or 2.4 GHz?