Shadowing Loss
Shadowing loss is the extra attenuation in the region behind a large obstacle such as a building, container, load or machine body. It adds on top of the free space path loss and, depending on the size and material of the obstacle and the distance, can typically exceed 10 dB. Its difference from multipath fading is that it changes slowly on the scale of metres.
While fading fluctuates on the scale of centimetres, shadowing changes on the scale of metres. When you move behind a container the signal drops gradually and stays low as long as you remain in that region.
- Most common source: the operator's own body. Putting the remote control between the body and the receiver costs a few dB.
- Industrial sources: the load, the bucket, the crane boom, a truck trailer, a steel column.
- Frequency effect: lower frequency leaks further into the shadow by diffraction, so sub-GHz is advantageous in the shadow region.
The counterpart on the installation side is clear: put the receiver antenna at the highest and most open point where the machine body will not shadow it. On the operator side, holding the remote control in front of the body rather than behind it, leaving the antenna free and not gripping it in the palm makes a difference. In AXI sets the receiver antenna being movable outside the enclosure through a cable gland is exactly for reducing this loss.
Context where this term is used: Wireless remote control installation: pairing, relay, safety