Why In Figure T-3 the item labeled 4 is drawn as a vertical line topped by two diagonal lines forming an open V, which is the standard schematic symbol for an antenna. It sits at the output end of the circuit, which is where a transmitted signal is radiated. Figure T-3 is a simple transmitter chain, so the last element after the filtering and amplifying stages is the radiating element.
Watch out The ground symbol is easy to confuse with it, but ground is drawn at the bottom of a circuit as a stack of shortening horizontal bars or a solid triangle pointing down, not an open V pointing up.
Open V pointing up and out equals antenna radiating; stacked bars pointing down into the earth equals ground.