Can anyone help a newbie installing a J-Pole antenna.

Antenna: Copper Pipe Dual Band 2M/70CM. Bottom of long leg is tee. lower leg
of tee goes 14" w/ 1/2" copper then transitions to 1" x 36". This is clamped
to two tv mast mounts, anchored to a wooden chimney chase.

When I built the antenna, it displayed a relatively flat SWR across both
bands, using an MFJ-269. Antenna was free standing in yard, away from
anything to affect it.

After mounting, the SWR seems to vary from as measured (1:1.2) to off the
map. Thought it was maybe bad coax (LMR-400) but as I checked it, the SWR
came back into line. Someone told me to ground the lower end of the j-pole,
as if it were clamped to a tower. I did this and the SWR goes off the map.

Should a J-pole be grounded? if not, how do you protect it or the structure
from a lightning strike?

Thanks

Paul P