Well I will take ownership of this one, since I was the one who told you to buy it. It worked great on my 4300, so I assumed it would work on a 4500, and while it still might, I shouldnt have made that assumption with my accurate testing, and I am sorry.
Now lets get down to buisness:
Hardware
DGL-4500 A2 with 1.22NA
DWL-AG530 driver 5.3.0.46
Network Configuration
802.11G Only at 2.4Ghz
Auto Channel Scan on
Transmission Rate - Best
WPA2-PSK with AES
WMM Enabled
Short GI On
Extra Wireless Protection Off
DWL-AG530 all settings set to default.
Location
The router is located about 10-12 feet above the adapter, directly under it, but with a brick wall (the front of my house on the first floor) next to the wireless desktop.
Results
Using the Status > Wireless page for a semi accurate Signal % I get around 80-90%. This does change quite frequently too, whether that normal or not, I do not know. For the sake of this test, we will call the antenna closest to the power cord A, the one in the middle B, and the one furthest from the power cord C. The first thing I did was remove all the antennae and was surprised I still got a signal of 17%. Then when I put in C, it went to 24. I unscrewed C and just screwed in B, and got about the same. I then unscrewed B and screwed in A, and it jumped to about 70-72%. I unscrewed A and just screwed in B and C and got about 40-45%. And with A and C, it was still around 70%.
Hypothetical
So I think Antenna A(closest to the power cord) is the domminent broadcaster while in G. With maybe radio assist from C? Where my question is, when does NIMO go into effect? Theres no setting to turn it on or off, so I assume its always on? But if the connection can still be active with one antenna, maybe it adjusts automatically? Because I don't see how you can get NIMO with one antenna.
Suggestions
Put the extender closest to the power cord. Also try enabling and disabling the Short GI and the Extra wireless protection. Also, if you have Android OS phone, download a free app called "WiFiScan". Not only does it tell you your channel, it gives you a portable platform with a DB read out on signal strength, which is great for finding the best place for a antenna on the receiving end. It also helps in the orientation of the antenna. I laptop will do as well, just don't pay any attention to the bars, since they are not accurate at all.