Digital Matter Cellular devices report their cellular signal strength in Analogue 4 by default. The value reported is the signal strength seen at the beginning of the previous connection attempt. The best way to check for a signal strength problem is to graph the value of Analogue 4. On Telematics Guru, this can be done with the Asset Analogue Graph Report:
Reports > View All Reports
Asset Analogue Graph.
When you download the resulting spreadsheet, it will have the data points in one sheet, and a graph of the selected analogues on another which could look something like the following:
The value reported usually ranges from 0 to 31, and is interpreted as follows:
0: -113 dBm or less
1: -111 dBm
2: -109 dBm
30: -53 dBm
31: -51 dBm or greater
As shown below from uBlox's R410 documentation:
The threshold of usability is about 2, and strengths reach 31 easily when close to a cellular tower. However, were the antenna to snap off, you could expect the value to drop by 20-25 (40-50 dB). It would still be possible to connect when close to a tower, but the communications range would decrease by a factor of roughly 100.
If your signal strength graph shows very low average values, and peak values lower than 15, despite the device being in an area with good coverage, it is reasonable to suspect an installation problem or a hardware fault.
- Check that the unit is installed in a location where its antenna will be effective
- Not inside a sealed metal box
- Not inside a 360 degree metal mesh enclosure with openings less than 20 cm wide
- Not right next to a source of electrical noise (certain cheap electronics, brush motors)
- The higher the better
- Examine the PCB for cracks in the solder at the antenna attachment points:
If you suspect a hardware fault, and the unit it is still under warranty, your distributor will be able to help you with further debugging, repair, or replacement.