Bizarre Challenge

I currently have a Netgear WGR614 v9 Router and WG311 v3 Wireless PCI Adapter. They are two rooms apart. I used to have a good signal strength when I used to use a Sitecom router and adapter, but now I can barely receive any signal. Quite often I have to reposition the router, or try repairing my connection to get a 'very low' signal at just 1 MBPS. It's capable of 54 MBPS. It makes no sense that the signal is so weak. I tried attaching a larger 9dB antenna to the PCI adapter but I get the same results. Unfortunately the router is a sealed unit and it is impossible to replace the antenna on that. I've tried my PCI card in different slots, I've checked the router and PCI card for firmware updates, and I've tried to connect to the internet by the software that came with the card and also through XP zero facility. Sometimes it just about connects to the router but fails to give me any internet. At best, after a few attempts of repairing the connection I will get a 'very low' signal at 5.0 MBPS, but this is becoming more rare. When I look for available networks it shows the signal strength of my home network as being approximately 50%. It's bizarre. I've tried encypting and not encrypting the network, I've tried every channel on the router. I'm running out of ideas. I've plugged in just the router (no internet) next to the PCI card and it instantly connects with 'excelent' signal on 54 MBPS. All that stands between the router and the PCI card when in the separate rooms is a hallway and partially a bathroom. Nothing big and metal. If anyone has any ideas as to how to rememdy this, I'd be very grateful. Thanks for reading. Lewis