Scanner help for a newbie radio user?

[10aila]

I have a Radio Shack PRO 404 scanner, and I would like to set up an external antenna because the one that the scanner came with is terrible unless you're real close to the signal source. I was considering a dipole type thing, but I know a tiny bit about radio theory and I know that antenna length and frequency are connected. I want to have good performance across the spectrum that my scanner recieves. The lowest band my scanner recieves is 20 meter ham or 29 mhz, so I was going to build a 10 meter long antenna and hope for the best, but will this have good reception across the spectrum?