In my home, we get internet and TV both over an optical fibre.
The setup is, this
Optical terminator -----Router----Switch---Set top box---TV--Wii U | | | \---WiFi Access point | \----Set top box/PVR
All links shown are ethernet, except the links to the TV, which are HDMI. There is also a WiFi link from the access point to the Wii U and to lots of devices not shown.
Now, most of the time, the WiFi (802.11n at 2.4 GHz) works fine. It works, for example, when the PVR is recording or playing back, or even when it is both recording and playing back. It works when watching netflix via a Wii U (which is good, since the Wii U uses WiFi.)
But when watching live TV, the performance of the WiFi usually drops from about 100Mbps to about 1Mbps and often connections are dropped. I've noticed that, if I pause the TV for a few seconds and then play (so the PVR acts as a buffer), this will get the WiFi working well again.
Curiously if I connect a computer to the switch directly there is no performance problem at all. Furthermore there doesn't seem to be a problem at 5GHz, only 2.4GHz.
The TV itself is not part of the problem. I can turn the TV on or off without affecting things one way or another.
So my question is, what could be causing the WiFi performance to drop dramatically when the set top box is outputting live TV is on, but not in other circumstances?