Line-of-Sight Range
This is the working distance measured under conditions where there is no obstacle between transmitter and receiver and the line of sight is clear. The roughly 150 m figure for AXI's ST series sets and the roughly 100 m figure for the SF series apply to open-area conditions; indoors and behind obstacles the real distance stays below this.
Line-of-sight range is an upper limit, not a guarantee. The signal attenuates with distance in free space; every obstacle in the way adds a further loss on top of that attenuation.
The main factors that reduce the real distance:
- Reinforced concrete walls and steel structures: the reinforcement behaves like a grid, and the transmission loss is significant.
- Metal enclosure: if the antenna is inside the panel, the loss can be greater than the sum of all the other factors.
- Interference sources: inverters and arc welding raise the noise floor and shorten the effective range.
- Transmitter battery: a weak battery lowers the output level and therefore the distance.
The right approach is to use the catalogue figure as a comparison measure, not as a selection criterion. Determine the longest distance your application requires, add a margin for obstacles and interference, and choose a set whose catalogue figure is clearly above that total. During commissioning, test the range from the furthest point of the site with no load and write the result in the maintenance record; only with this reference will you notice a drop in range later on.
The context in which this term is used: 433 MHz or 2.4 GHz?