i just shortened my antenna about 1/2 because it looks cool and doesnt effect reception "too?" much. if your interested in doing so...
1. unscrew the antenna ccw out of mount.
2. score with a razor blade around the tip base on the shaft.
3. get a small pan of boiling water and put the tip into the boiling water for a 30 sec?, so you can pull the end off the shaft, "cough"
4. carefully cut the shaft with a hack saw as cleanly as possible. to the length you want.
5. gently twist the cap back onto the antenna in the direction of the wound wire.
6. if necessary put a drop of zap glue in the cap before installing.
7. stand back and look at your cool antenna and think how you just saved yourself a few bucks. it still receives about the same. i put a towell for a background in the pics so the antenna shows better.