Dualband: still connection problems on 5ghz

[heerp]

I bought a Netgear N 3700 dualband router, for avoiding disconnection when using my cordless phone. When connected through the 5 Ghz channel, I continue to have disconnections when calling. What could be the real problem here?

 

[heerp]

Edit: The problem seems however to be caused by the new Netgear MODEM (red LED indicating internet disconnection).

I do have a splitter in place.