Internet speed drops. How to find the reason?

Question

Computer networks

Hi friends.
The problem is this: periodically, without any regularity, the speed of the jump drops to ~ 4-5 Mbps.
Router TL-WR740N, Firmware 3.13.2 Build 140814 Rel.39331n
PC: Win 8, Intel i5-3230m, 8GB RAM, HDD 5400 rpm
WI-FI: Qualcomm Atheros AR9485WB-EG, Driver 10.0.0.263
Chrome and Firefox show ~same values ​​on www.speedtest.net
Only disable/enable Control Panel\Network and Internet\Network Connections\Qualcomm Atheros AR9485WB-EG Wireless Network Adapter helps. Which, as it were, hints that the provider has nothing to do with it, because. it's worth rebooting the network connection or PC and everything falls into place (~ 100Mbps)
I checked it for everyone with the help of CureIT, AVZ and NOD32 - no crime.
Help, pliz, how to find out where the root of evil lies?

Answer 1

first, check on the local network how it will work, Wi-Fi may fall off from the congestion of the channel, and when you reboot, your access point may choose a freer channel and the connection will be established again. But anyway, first of all - through the postings we will check the speed