Keep losing internet connection

I have had the same issue and managed to sort it out somewhat by changing from mixed mode to just 802.11g mode only. Does using this 'G' limit the speed of the network?I haven't had any issue with any of my other Apple products using the mixed mode on my wifi but only my Mac computer. Any solutions for this? This is a detailed description of the problem.

I own a iMac 27 inch model number ......... and after the Sierra iOS update, I have an issue with the wifi access. The internet connection keeps dropping out every few seconds continuously. When running the diagnostics, ISP, Server and Internet stays in the red, connects momentarily green and then disconnects again. Note, the wifi doesn't disconnect though. I tried all possible remedies online except for changing the wireless mode from mixed mode of 802.11 to 802.11g only. This worked. However, before I connected the Apple Mac to this router all my other computers in my house including my apple iPads and iPhones all worked without any issue including my wireless printer. I cannot understand why only my Apple Mac computer doesn't connect on mixed mode and only works on 802.11g mode only. Even changing the wireless router itself didn't help and also I changed to the airport express 802.11n and still did the same unfortunately. As of present I am using the above mentioned wireless router which is with the fibre optic connection and the settings as shown above. The internet connections stays steady with these settings on the Apple Mac.

Has anyone had this similar issue? Does apple have a solution for this. I feel its something wrong with the computer software itself and noticed this after the Sierra iOS upgrade. Could anyone suggest a possible solution for this and using only the G mode, does it slow down the wifi connections speed unlike when using the mixed mode? I tried all possible solutions other than the one and only changing of the mode to only 801.11g mode and that's the only thing which makes the connection stable and doesn't let it drop out.

I've had non-stop problems with internet connectivity starting in May 2016, and really shaking my faith in Apple. Out of the blue in May, I stopped connecting. Everything was fine before that. My MacBook Pro had no internet at home, but had no problem connecting at Best Buy, the Apple Store, the library, and the coffee house. AT&T said it was my MacBook; Apple said it was my router. The only solution I could see at the time was to dump AT&T and switch to Charter, which I did, also purchasing a new router (a combo modem/router) for good measure. That seemed to fix it, at least until October. Internet starting to freeze again, and every time I would run a Network Diagnostic it would free it back up. But I would be doing that sometimes as often as 10 times in 2 minutes. It varied. My frustration with that, coupled with my frustration with Sierra, led me to trade in my MacBook Pro for a 2016. But it had the same issues! So I decided to replace the router AGAIN. Charter and AT&T both provide customers with straight modems so I decided to replace my modem with a compatible coaxial router/modem combo. When I did that I lost connectivity to ALL devices in the house (iPhone, iPad mini, Apple TV). At this point I decided to use a router and a modem as 2 SEPARATE DEVICES and decided to purchase YET ANOTHER router! (If using separate devices is the norm it was NEVER explained to me.) So last night I purchased an AirPort Extreme. Set-up was easy and Apple provides prompts for set-up (which it DOESN'T provide for the installation of other brands of routers.) It took about only 5 minutes, having to reset, turn off and on, and remove the ethernet cable from my modem. So now 8 months, 24 hours and $1700 later, I FINALLY have seemingly solid connectivity. For now.....