Overview:
John Mills, an engineer at the Western Electric Company, shares his knowledge of radio technology with his son, J.M., through a series of letters written in 1922. The book starts with a fundamental explanation of matter, introducing the concept of electrons and protons as the basic building blocks of the universe. He then delves into the workings of copper wire as a conductor of electricity and explains the functioning of batteries, both dry and wet cell types.
He then introduces the audion, a revolutionary vacuum tube, and explains how electrons are emitted from a heated filament and subsequently manipulated using a grid. Mills describes how to measure currents, voltages, and resistances, providing practical examples and illustrations to simplify complex scientific concepts. The book further explores the use of coils and condensers in circuits, highlighting their role in controlling frequency. It culminates in a comprehensive explanation of radio telephony, including the transmission of voice signals and the intricate workings of various detectors, like the audion and the crystal detector.
Key Findings:
- Electrons and protons are the fundamental building blocks of matter.
- The behavior of electrons in various materials and circuits is crucial to understanding electricity.
- Vacuum tubes, especially the audion, revolutionized radio technology.
- Tuning circuits using coils and condensers is fundamental to radio communication.
- The human voice can be modulated and transmitted using radio waves.
- The regenerative circuit, with its feedback mechanism, allows for efficient signal detection and amplification.
- The super-heterodyne system utilizes intermediate-frequency amplification for sharper tuning and greater amplification.
- Carrier current telephony allows multiple conversations to be transmitted simultaneously on the same wire pair.
Learning:
- The nature of matter: The book explains that all matter is composed of atoms, which are made up of electrons and protons. This basic understanding of atomic structure is essential for comprehending the behavior of electricity.
- The workings of batteries: The letters describe the chemical processes involved in generating electricity using both dry and wet cell batteries. This knowledge is helpful in understanding how electronic devices are powered.
- The audion and its applications: Mills provides a comprehensive explanation of the audion, a vacuum tube that revolutionized radio technology. He explains its operation as a detector, amplifier, modulator, and oscillator, highlighting its versatility in various radio applications.
- The principles of tuning: The book explores how to adjust the frequency of radio circuits using coils and condensers. This knowledge is crucial for optimizing the reception and transmission of radio signals.
- The intricacies of radio telephony: The letters offer a detailed explanation of radio telephony, covering modulation, detection, and the role of the human voice in radio communication.
- Amplification at intermediate frequencies: The super-heterodyne system is described, demonstrating its advantages for sharper tuning and higher amplification in radio reception.
- Multiplex telephony and telegraphy: The book delves into the concept of carrier current telephony, explaining how multiple conversations can be transmitted simultaneously on the same wire pair.
Historical Context:
The book was written in 1922, a time when radio technology was rapidly evolving. The audion, a relatively new invention, was transforming radio communication, enabling the transmission of voice signals and paving the way for broadcasting. The development of vacuum tube technology was a significant advancement, leading to improvements in sensitivity, power, and range of radio communication. The use of carrier currents for multiplex telephony was also a breakthrough, laying the groundwork for modern telecommunications.
Facts:
- Hydrogen atom: The simplest atom, composed of one proton and one electron.
- Helium atom: An inert gas with four protons and four electrons, used for filling balloons.
- Air composition: Mainly nitrogen (78%) and oxygen (20.8%).
- Earth composition: Mostly oxygen (47.3%) and silicon (27.7%).
- Seawater composition: Primarily oxygen (85.8%) and hydrogen (10.7%).
- Atomic number: The number of electrons in an atom, which also indicates the number of protons in the nucleus.
- Copper atom: Has 29 electrons and 29 protons.
- Ions: Atoms or parts of molecules that have gained or lost electrons and carry a net electrical charge.
- Dissociation: The process of molecules breaking down into ions when dissolved in a liquid.
- Electrolytes: Substances that dissociate into ions when dissolved in a liquid.
- Electrodes: Pieces of metal or wire that control the flow of electrons in a circuit.
- Ammeter: An instrument that measures the flow of electrons in amperes.
- Volt: The unit of measurement for electromotive force, which drives electrons in a circuit.
- Ohm: The unit of measurement for the resistance a circuit offers to the flow of electrons.
- Condenser: A device that stores electrical charge, made of two conductive plates separated by a non-conducting material.
- Inductance: A property of a circuit that opposes changes in the flow of current, particularly in coils of wire.
- Henry: The unit of measurement for inductance.
- Microfarad: The unit of measurement for capacitance.
- Wave length: The distance traveled by an electromagnetic wave during one cycle of oscillation.
- Frequency: The number of cycles of an alternating current per second.
- Speed of light: Approximately 186,000 miles per second or 300,000,000 meters per second, also the speed of radio waves.
- Resonance: A condition where two circuits oscillate at the same frequency, resulting in maximum energy transfer between them.
Statistics:
- Atoms in a small copper wire: Billions
- Electrons emitted per second from a red-hot filament: Billions
- Electrons flowing through a 40-watt light bulb per second: 2.5 billion billion
- Electrons flowing through a wire carrying one ampere of current per second: 6 billion billion
- Electromotive force of a dry cell: 1.46 volts
- Electromotive force of a fully charged storage battery: 2.4 volts
- Frequency of household electricity: 60 cycles per second
- Frequency of radio signals used by ships: 500,000 or 1,000,000 cycles per second
- Frequency of signals from spark transmitters: 1000 signals per second
- Speed of sound in air: 1100 feet per second
- Frequency range for natural speech reproduction: 200 to 2000 cycles per second
- Range of wave lengths needed for voice transmission at 50,000 cycles per second: 5770 to 6250 meters
- Range of wave lengths needed for voice transmission at 500,000 cycles per second: 598 to 603 meters
- Number of simultaneous telephone conversations possible using carrier-current telephony on a single wire pair: 5
- Number of simultaneous telegraph messages possible using carrier-current telegraphy on a single wire pair: 10
- Number of repeater stations used in a telephone circuit from New York City to San Francisco: About a dozen
Terms:
- Atom: The smallest unit of an element, composed of a nucleus and electrons.
- Electron: A negatively charged particle that orbits the nucleus of an atom.
- Proton: A positively charged particle found in the nucleus of an atom.
- Ion: An atom or molecule that has gained or lost electrons and carries an electrical charge.
- Electrolyte: A substance that dissolves in a liquid to form ions.
- Electrode: A conductor, usually made of metal, that controls the flow of electrons in a circuit.
- Ammeter: An instrument that measures the flow of electrical current in amperes.
- Volt: The unit of measurement for electromotive force, which drives electrons in a circuit.
- Ohm: The unit of measurement for the resistance a circuit offers to the flow of electrons.
- Condenser: A device that stores electrical charge, made of two conductive plates separated by a non-conducting material.
- Inductance: A property of a circuit that opposes changes in the flow of current, especially prominent in coils of wire.
- Henry: The unit of measurement for inductance.
- Microfarad: The unit of measurement for capacitance.
- Frequency: The number of cycles of an alternating current per second.
- Wave length: The distance traveled by an electromagnetic wave during one cycle of oscillation.
- Resonance: A condition where two circuits oscillate at the same frequency, resulting in maximum energy transfer between them.
Examples:
- The game of tag: Used to explain how electrons and protons interact to form atoms.
- A boy’s wagon on a hill: Illustrates the concept of a reversible battery, comparing the energy stored in a battery to a wagon rolling downhill and the charging process to pushing the wagon uphill.
- Rude boys on a crowded sidewalk: Used to describe how electrons bump and jostle against atoms in a wire carrying a current, generating heat.
- Boiling water: Explains the process of electrons being emitted from a heated filament, similar to the evaporation of water molecules from a heated surface.
- The boy’s conscience: Illustrates the concept of self-inductance, comparing the self-induced effect of a coil opposing changes in current to a boy’s conscience hindering his actions.
- Two boys with a hedge: Used to explain the principle of electromagnetic induction, where the motion of electrons in one coil induces a current in a neighboring coil.
- A city map: Used to visualize the relationship between grid voltage and plate current in an audion, demonstrating the audion characteristic curve.
- A boy’s money: Used to explain the concept of resolving a complex signal into its component frequencies.
- A vibrating string: Demonstrates the relationship between frequency and pitch, and how a complex sound can be broken down into its component simple vibrations.
- An organ pipe: Illustrates how the shape of a resonating cavity affects the sound produced, similar to the human mouth cavity.
Conclusion:
John Mills’ “Letters of a Radio-Engineer to His Son” is a fascinating and informative guide to the fundamentals of radio technology. From the basic building blocks of matter to the complex workings of radio telephony, the book provides a clear and engaging explanation of key concepts. By understanding the principles of electron flow, tuning circuits, and signal modulation and detection, readers can gain a deep appreciation for the science behind radio communication.
The book is particularly valuable for its historical context, offering a glimpse into the early days of radio technology and highlighting the revolutionary impact of the audion. The detailed explanation of various circuits, including the regenerative circuit and the super-heterodyne system, reveals the ingenuity and innovation that characterized the development of radio technology in the early 20th century. While technology has advanced significantly since 1922, the fundamental principles outlined in this book remain relevant and provide a solid foundation for understanding modern radio and telecommunications.