Mac Mini 2011 built in Airport
OK, a slight semantic issue. Thanks to Apple, the "Airport" I am referring to is the hardware/WIFI
router that Apple sells, not the WIFI capabilities that is in their computers. The built-in hardware is better referred to simply as WIFI (or wifi), it's pretty generic, not much different than in any other computer. In earlier hardware, it actually was a separate plug-in card, thus it picked up the "Airport" name; just marketing, IMHO.
So, the only Wifi modem/router is the one from Netgear and it is wired directly to your cable (or satellite/DSL) modem. Since you probably don't have another wifi router sitting around it will be fairly hard to determine the exact cause of the drop outs.
Wifi is not the most stable of communications protocols, being affected by radio interference from everything from microwave ovens to black helicopters flying by!
Pity the owner of a plaster walled home; all that metal mesh makes a good Faraday cage!
I don't suppose there is another Ethernet out from the Netgear or the Time Capsule that could connect the Mac? On the other hand, even Ethernet
switches are inexpensive and they can provide at least 4 or 5 outputs for the smallest ones. Wires are still faster than wifi (unless you have the latest) and don't have the radio interference problems. Of course, it's sometimes hard to find an invisible path for the wire from one room to another.