If you are very confident in your soldering skills I recommend that you open the Rx case and replace the entire antenna from where it begins on the internal circuit board, just make sure that your new wire is EXACTLY the same length as the old antenna. This will be a stronger and more reliable repair. And absolutely do not fly on that Rx again until you have performed a thorough range check.

This happened to me awhile ago. I didn't have the cut off piece to reference the proper length. What I did was make the RX antenna the same length as the TX antenna. Worked great for me, never had a problem after that .

I found a nice set of instructions with photos on this proceedure here http://www.rccentral.com/qanda.asp?ATCL_ID=49 . They're talking about a car receiver, but it's exactly the same for planes.

Good luck!