Time on Air
Time on air is the duration for which the transmitter is transmitting a single packet, and it is calculated from the packet length and the data rate. This duration determines two things: how fast the duty cycle budget is used up, and how long the channel stays closed to other devices. A short packet both spends less budget and stays exposed to interference for less time.
Roughly, time on air is the total number of bits divided by the data rate. A 32-byte packet stays on air for about 26 milliseconds at 10 kbit/s; the same packet takes ten times as long, about 256 milliseconds, at 1 kbit/s.
- Budget effect: the duty cycle limit is defined as total transmission time per hour; long packets fill that total quickly.
- Interference effect: the longer a packet stays on air, the higher the chance it is hit by an interference burst within that time.
- Channel occupancy: if there is more than one transmitter on the same site, long packets raise the probability of collision.
That is why the payload is kept short in remote control design: a few bytes of address, button state and checksum. Sending a short packet at defined intervals instead of transmitting commands continuously both protects the budget and makes multi-set operation possible.
Context where this term is used: Wireless remote control installation: pairing, relay, safety