Vigor routers gather information about the detected signal strength of a connected 3G modem by using the AT command: AT+CSQ. In the example above, the resulting signal strength is “CSQ:X,99 OK”, in which X is the signal strength calculated using the formula – X/31 x 100%. Here the signal strength ratio came to 15/31 which is 48%.
Now, here we used the Huawei E220 which displays the parameters correctly. While most modems can also display these parameters, some cannot (for example the C- motech CNU-680). In these cases the signal strength value will not be shown but instead displayed as “-“.