I desoldered the old, fixed antenna, and replaced it with a removable antenna.
I tested it out, and it works fine, if not better than the old one. Even though “better” is subjective, signal strength to my other router went from -87dBm to -53dBm, both with -99dBm noise.
Note, I had to mount the antenna in a different hole than the previous one, because there were parts in the way of the antenna mount.
This photo shows you the location of the solder points for the antenna. The “tip”, or center of the antenna wire, is a little longer than the braided shield, and is soldered to the point marked “Tip”. The shield is just soldered together onto the portion marked “Shield”.
In other words, put it back in like you took it out, and make sure there’s no solder connecting the tip and shield parts. It tends to burn up your chipset. 🙂
Well, here is my WRTSL54GS’s new antenna, liberated from an old BEF-11.