Originally Posted by LIScanner101
Would one just increase the main long element proportionally to achieve VHF low (30-50MHz) coverage and, if so, would this be detrimental to VHF high?
You may want to add a section for VHF-Low instead of changing the VHF-Hi to VHF-Low if you still want VHF-Hi coverage. I would make the current 19" section the correct length for your VHF-Low area of interest (say around 72" for 39 MHz) and add a stub for VHF-Hi that's about 1 1/2" away from the center stub and 19" long, mounted as close to the base as possible. I'd actually make it using the same piece of wire as the 6" UHF section (6" down, 1" over, loop around the center pin, 1.5" over, 19" up). I'd also look for some brass welding rod for the VHF-Low section due to the length (if you can find it that long). The brass will give you better strength.
Don't forget to extend your ground-plane elements to be sized for the lowest frequency (longest element) in your antenna. For VHF-Low, you probably want them out of brass welding rod as well for strength.
Modify lengths as necessary for optimum performance on each band. Since each band has their own element, this should be fairly easy to do. Pay special attention to the 800 MHz element if you modify it since where it attaches to the main element will also need to be adjusted.