Why is it that a transistor radio gives a clear and loud reception

The antenna of a transistor radio is the first stage which collects the radio signal of all frequencies from the surroundings.

This is further processed in the tuning circuit of the set in order to choose the desired station, followed by carrier filtration and amplification before it is fed to the loud speaker in order to convert it to the audible sound.

The clarity and loudness of the audio depends, among many other factors, on the strength of the signal received by the antenna.

This is enhanced if the signal collection area is increased. It is a common experience that a long stretched conducting wire or a spread out conducting object, acts as an effective signal enhancer when connected to the antenna. Our body has finite conductivity and for many purposes can behave like a conductor.

Thus, when we touch the antenna of an operating radio set, we increase the effective signal collection area and thereby the signal strength gets improved and the loudness increases.

Further, even if the antenna rod is covered by a layer of insulating paper and we hold the rod around this paper, the very high frequency (radio frequency) signal collected by our body is gathered, to a lesser extent, by the antenna due to capacitive coupling even though there is no direct conducting contact of our body with the antenna rod.