We replaced our Cisco 877W with a brand new UC-540 from Cisco in January 2010.
We setup the UC-540 via wizard. Upon use, we immediately noticed a decrease in wireless signal strength and dropped connections every three minutes or so - even when within feet of the device when compared to the Cisco 877W.
We first attributed the issue to the slightly more enclosed mounting location, or the additional metal shelving. . We were just about to pay for a professional site survey to rule out radio interference when we discovered a a reference from http://uc500.com/en/uc520w-built-wifi-fluctuating-rf-levels.
We decided with Cisco's STAC to test the following solution before RMA'ing the unit as faulty;
antenna receive right
antenna transmit right
It worked! Our signal strength is much better and we have yet to drop a connection after two weeks of regular use.
Did Cisco fail to consider that there is only one antenna in this device?