AirPort and the Motorola SB6190 are hardwired to my iMac.
If you have not changed out the Ethernet cables between the modem and the Time Capsule, and the Time Capsule and your iMac in 4-5 years or so, that would be recommended.
If you don't want to swap out the cables, at least pull out the plugs and then plug them back in a dozen times or more to help knock off any corrosion that may have built up on the tiny copper contacts on the plugs and ports on the modem and Time Capsule.
Two Mac laptops and two iPhones use the wifi.
Do these devices also lose the signal when the iMac does? Or, do the WiFi devices stay connected when the iMac drops?
If both the iMac and WiFi devices lose connection, then it would be a good idea to "test" your Internet connection by temporarily connecting the iMac directly to the modem for a day or two to see if the Internet drops still occur.
If the Internet connection remains stable during your "test", then that would indicate that your Internet signal coming into your house is good, and the modem is operating correctly as well.
However, if you still see drops during your "test" then that may indicate an Internet connection issue from your provider, or the modem may be starting to act up.
Unfortunately, intermittent issues are always the toughest challenges, so it will likely take some time and patience to figure out where and what the actual issue might be.
Average useful life of a Time Capsule is about 5 years, so there is that to consider as well. If the Internet connection and modem check out OK during your direct "test" with the iMac, then the focus of attention moves to the Time Capsule.
Personally, I would not keep any data on a 7-8+ year old Time Capsule hard drive that I could not afford to lose, because the Time Capsule hard drive also becomes "suspect" at about 5 years.
