I have bt infinity modem connected to a ASUS RT-ac56U router it is working ok when i am using my mac book pro on 5ghz wifi but my prom is with my wife's laptop with windows 7 on it and only 2.4 ghz wifi if i reboot the router and do a speed test i get 34mb/s but after a minute it drops down to about 2.3 mb/s that is a big drop of over 31mb/s. and by resetting the router it will be back up at 34mb/s for a minute or two and then drop.
On my mac running on 5ghz i get about 61mb/s and it stays at that as long as i am on it
so why is this not so with the windows laptop with 2.4ghz wifi???