10/100 and 30Mbps Internet

Hi All.

I have a 30Mbps internet connection. I connect my cable modem directly to my pc's 10/100 ethernet card and get as good as 30Mbps. So far, so good.

However, when I connect the cable modem to my D-Link DI-614+ and then run a cable from one of its 10/100 Ethernet ports to the PC's Ethernet

I called D-Link support which I think is in India. They're advice? Turn of my microwave oven. I am not kidding.

Is it because the router is wirelessly broadcasting the signal or is it due to some limitation of the router?

Any help is much appreciated.

Neil