What's your reading on ch19? usually you can get a pretty balanced bell curve if you dial in channel 19. I got a 1-1.1 on 19 and 1.3-1.4 on ch1&40. Those numbers sound great.

 

You're in the money. Just like Sin suggested, dial up channel 19 or 20 and take a SWR reading at that point just for curiosity sake. If it were me, I'd reinstall the tunable tip trimmed to say half it's current length. Or take a more conservative approach and go 1/4" at a time. Trim it shorter each time checking the SWR at 1, 20, 40. If you start seeing no change in the SWR readings, put the cap back on the antenna, and pop the cap off the beer bottle and admire your work. Your done at that point. Make sure that when doing these checks you keep putting the rubber tip back in place for consistency. Also, you could end up with the tip trimmed so short that all that's left is the small knob just sitting on top of the antenna shaft. That's cool. Remember, it's all FM..............F@%$in Magic anyway. Now go and enjoy a cool one!

 

That particular antenna is the Wilson no ground model. The wire coming off of the bottom of the antenna most often does NOT need to be connected to anything. Try disconnecting it and check your SWR again.

The antenna should be tunable even if it doesn't have a brass knob on the top. It's just that you have to cut it down to match it.