You can check www.antennaweb.org to see which stations you should be able to pick up. It will also tell you what kind of antenna you should get. (Since you already have an antenna, you can see if you have the right kind.)
Even the best antenna in the world won't be able to overcome obstructions in the signal path: tall buildings, hills, trees, mountains, etc. But free TV is hard to beat, given the general mediocrity of most cable programming.
Violet is extremely weak signal, so thats why it would be hard to find an antenna to receive it. If its a UHF channel, your best chance would be with the larger highest gain Channel Master model 4228 8x bowtie antenna plus the Channel Master model 7777 preamp. Even with that solid reception isn't guaranteed, but its the best chance for it.