1. Antenna: The radio starts with an antenna that receives radio waves from various broadcasting stations. These radio waves carry information in the form of amplitude modulation (AM) or frequency modulation (FM).
2. Tuner: The antenna picks up a wide range of radio waves, but to hear a specific station, the radio needs to tune in to the desired frequency. The tuner circuit, consisting of capacitors and an inductor, acts as a frequency selector. It allows the radio to resonate at the frequency of the station you want to listen to while rejecting other signals.
3. RF Amplifier (Radio Frequency Amplifier): The tuned radio waves at the selected frequency are very weak when picked up by the antenna. The RF amplifier stage amplifies these weak signals to a stronger level before sending them to the next stage.
4. Mixer: The mixer circuit combines the amplified radio signals with a locally generated frequency known as the "local oscillator" signal. The mixing process creates intermediate frequency (IF) signals that contain the desired audio information.
5. IF Amplifier: The IF amplifier further amplifies the intermediate frequency signals while narrowing down the bandwidth to reject unwanted frequencies.
6. Detector: The detector stage demodulates the IF signals to recover the original audio information. In the case of AM radio, this involves rectifying the amplitude variations of the signal, while in FM radio, it involves detecting the frequency variations.
7. Audio Amplifier: The recovered audio signal is usually still quite weak at this point. The audio amplifier stage amplifies the audio signal sufficiently to drive a speaker or earphone.
8. Speaker: The amplified audio signal is sent to the speaker, which converts the electrical signal into sound waves that you can hear.
By utilizing the process of amplification, filtering, detection, and amplification again, valve radios are able to capture, select, and amplify radio waves, demodulate the audio information, and convert it into audible sound.