For those of you who have wifi that works perfectly all the time; Lucky you! For the rest of us, I have done some research and wish to share some of what I have learned.
Simply enough wifi is wireless internet via radio signal; as such, it works great if you are in direct sight of the signal source and less well otherwise. Wireless a,b,g,n (standard wifi) all operate at 2.4ghz radio frequency; so do cordless phones, microwave ovens, some remote controls, bluetooth devices, and IOT (internet of things) devices. Wireless Dual Band and wireless ac wifi (the newer standards for wifi) operate at 5ghz and 2.4ghz or (under user control) at just 5ghz; some cordless phones (expensive, new) and broken microwave ovens can emit 5ghz signal (if your microwave significantly interferes with your wifi, it would be a good idea to consider replacing that microwave – it can mean its radiation shielding is breaking down). In the future I expect to see a lot more devices using 5ghz transmission; but, not in the narrow band used for wifi. As a rule of thumb. A given quality of signal (speed and reliability of wifi) requires half as much power at 5ghz as it does at 2.4ghz; radio signals at these frequencies do not bend, do not go around corners (thus my earlier comment about being in direct sight); but, they do bounce off some materials and will penetrate with some loss others.
What will wifi signals bounce off? Most metal surfaces, some types of rock (generally with metallic content), foil backed insulation, aluminum foil, tin cans and similar objects. What will wifi signals go through? Most wood surfaces and structures, craft-backed insulation, plastic encapsulated insulation, bare fiberglass, rockwool, paper based insulation, and, to a lesser extent, gypsum board (sheetrock). What will simply block wifi signal? Brick, tile, adobe, rock, cinder block and similar materials are excellent at blocking most radio signals including wifi. Of interest is that 5ghz will penetrate materials somewhat more readily than 2.4ghz and can work even after going through a 6″ adobe wall but with greatly reduced speed and reliability.
What do I do if I can’t get my wifi to cover the entire area where I want it? First, look at relocating the source (usually your wifi router); often you can get better coverage by moving it to a more central location. Second, try getting it up higher; on the floor all wifi behaves poorly. (I know I hate the trial and error method too; it takes time and effort). Next, you can try reorienting the antenna(s) on the router and, possibly, increasing the transmit power of the router (many routers have variable output settings -high,medium, low), or adding better antennas to your router. If you still don’t have what you want for coverage, you can use network over AC wiring devices (plug one device in next to your router and run a cable to it, then plug another one in near the device you want to have internet access and connect it by a cable from the plug-in device), or you can use one of the newer wifi range extender devices; these come in a wide variety in order to deal with most any situation. Sometimes it will take a combination of devices to cover a large building or area.
If you have a lovely southwestern adobe house, rejoice! You are pretty well protected from stray radio emissions, but your internal wifi area may be restricted to one or two rooms unless you are quite creative and go to some effort to expand your wifi area. In large homes it is often necessary to run network cable and use multiple routers to get good signal throughout; this is where a network or cabling professional can come in handy.