If the antenna is under you, and it is vertically polarized, then you need a
ground plane. That can be a metal disc 1/2 wave in each direction from the
coax. 1/4 wave is the distance it is tall.

I made a plate about 3/4 wavelength and that should reduce radiation
substantially.

I was at a meeting regarding ham radio antennas. Some woman testified that
she was afraid the ham radio antenna down the street was frying her brain.
Her proof that radio waves were bad was that most of the ham operators had
gray hari. During the break, she went outside, lit up a cigarette and got
on her cell phone.

Colin