For the ‘combination’ of a transmitting antenna, of height HT and a receiving antenna, of height HR, their ‘radio horizon’ equals x when HR = HT. Without changing the height of the receiving antenna, the height of the transmitting antenna is increased to 4 times its earlier value. The new value of their ‘radio horizon’ would be.
(1) 1.5x
(2) 2x
(3) 3x
(4) 4x