Scan wifi to locate periodic daily drops

My internet connection with Comcast drops off unexpectedly several times each day. When I check AirPort Utility it usually shows:

Internet: Off/No Connection. However, my Airport Time Capsule shows: On/Connected

I want to know how often and when these drops occur. I suspect the fault lies with the two-year old leased Comcast Modem, a Cisco Type XB3, Model DPC3941T with Voice Gateway.

By the time I call Comcast, the issue usually has resolved itself. When the agent remotely tests the connection all appears to OK.

Very frustrating!!!