Well if it's higher on 40 then it is on 1 it needs to be longer. That's the rule. if' you've tried it with the screw all the way out. Try it with a spacer or spring under the antenna. But first Try running the cable a different way. The smallest change sometimes can make a world of difference. Make sure your cable isn't coiled anywhere or overlapping. You want your cable as straight as it can be. How is your antenna mounted? How long is your coax cable? How far is it to your antenna from your radio. If you have to much coax that could be the problem. There are so many things it could be. So good luck and let us know. And If anything I've said here seems wrong to someone don't hesitate to jump in...lol I'm just stating what's helped me in the past.