Transistor Radio

 How does a transistor radio work?


Radio waves are electromagnetic (EM) waves generated by a radiating element (called Transmitting (Tx) antenna) and absorbed by Receiving (Rx) antenna.


An antenna is a conductor with a specified shape and geometry. Every free electron in the conductor is surrounded by an associated electric field. Whenever an alternating current flows through these passive devices, a varying magnetic field around the conductor is produced (Faraday's Law) and also the displaced electrons' shifts/ varies the associated electric field.


On the whole, due to the flow of alternating current, an EM field is created around the Antenna. This field of disturbance propagates through the media. The direction of propagation depends on the physical layout of the Tx antenna. For broadcasting purposes, Omni-directional antennas are most suitable.


The field strength of this EM wave (expressed in dBm/ dBW) depends on the amplitude of the current flow and varies inversely with the square of the distance between Tx and Rx antenna. Antennas are reciprocal passive devices, i.e., their operation as a receiving antenna is exactly the reverse of transmitting antennas operation. In receiving mode, the EM wave disturbance constitutes the flow of an electric current in the receiving antenna and this current contains the information sent by the Transmitter.


In radio broadcasting, two entities are involved. One is the transmitting Base station and the other is the receiving Transistor (colloquially a radio). In the Base station, the audio information is converted into electric current using transducers (e.g., Microphone) and this electrical signal, after modulating onto a high frequency carrier signal, is passed through (excites) the antenna which converts this electric energy into EM waves which propagates in free space and causes an EM disturbance in the Receiving antenna. As a result of this, an electric current flow through the receiving transistor and this current is demodulated to extract the original audio signal which is then amplified and played through a speaker.


This is how a transistor radio works in a nutshell. It is a fascinating device that allows us to listen to music, news, and other programs from far away places. Transistor radios are also very portable and durable, making them ideal for outdoor activities and emergencies. If you want to learn more about the history and science of transistor radios, you can check out some of these resources:

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