Bought a homebuilt once. Both radio antennas had been installed the same
way - with the cardboard drilling pattern glued to the aluminum - then left
there, and the antenna installed over the top of it. No ground plane.

The SWR was OK (1.8:1), believe it or not. It worked out to 10 miles or
so - then things started getting weak and scratchy.

Even a fancy Anritsu test set I borrowed from work showed no great problem.

But when I removed those drill patterns, things started working fine.