Siemens SCALANCE M874 Operating Instructions Manual page 41

Signal quality
During installation make sure that there is a good signal strength of > -73 dBm.
If the "Q" LED is lit permanently, the signal quality is good. For more detailed information,
refer to the section "LED display (Page 12)".
Avoid large metal objects in the immediate vicinity.
SCALANCE M876 antenna connectors
SCALANCE M874, M876
Operating Instructions, 06/2015, C79000-G8976-C331-05
Connecting up
3.6 Antennas
41