Greetings, I can't say that 17" is the most you'll ever get, but it is a fairly good output. As for the vinyl dielectric, I would skip it. Vinyl is the same as PVC, it's just that PVC is often thought of as being harder due to fewer plasticizers in it. PVC has a fairly high dissipation factor for RF, and isn't the best material. Have you looked in the yellow pages under plastic? That's where I've found my source. Chip