Here is a pic of my shortened antenna: 

All I did was eyeball it to see where the top of the truck was.  Then marked it, removed it, cut it down with a hacksaw. Then you can knock the ball off with a pair of pliers and then put it back on the top of the new end.  Then just reinstall and it looks much sleeker!  Another customization of BlackMagic & the Digital Electronics!

If you have any questions please let me know!