I agree with JC, an amplified antenna is not needed and could be overloaded by the strong signals. The documentation on the Philips web site offers very little insight into the correct way to orient the antenna, either in terms of how to aim or orient the antenna horizontally (which is the polarization common to OTA TV transmission).
So;
Have you tried installing the antenna outdoors?
Have you rotated the antenna in small (10° or less) steps to check for best signal strength?
Have you tried both vertical and horizontal orientation? The
manual and marketing photos generally show a photo that seems like the antenna is vertically aligned, which seems odd, I would expect to use horizontal orientation. Sadly, the manual is of no help resolving such a basic question.
The manual also refers to a gain control knob. Has that been adjusted to minimum?