Radio lecture part 1

Introduction to Wireless Communication

• The Telegraph (Invented $1840s$ by Samuel Morse)
  • Concept: Sending messages via cable using electrical current interruptions, interpreted as dots and dashes (Morse code).
  • Significance: Enabled much faster news and information dissemination.
  • Limitations:
    • $\text{1.}$ Vulnerability to Cable Cuts: If a cable between point A and point B was cut (e.g., "$\text{3,000}$ miles" between New York and Los Angeles), fixing it was time-consuming (days to locate, especially in "hostile territory" of the West).
    • $\text{2.}$ No Human Voice: Technology did not permit the transmission of human voice.
    • $\text{3.}$ Inaccessibility at Sea: Lack of widespread underwater cables (beyond the Transatlantic cable, which was not directly connectable for ships) meant ships were isolated from communication for "days, if not weeks" once leaving port.

Pioneering Wireless Theory and Proof

• James Maxwell (Theorist of Electromagnetic Waves)
  • Theories: Wrote extensively on the existence of electromagnetic waves or impulses that travel like light.
  • Hypothesis: Stated that radio waves, a part of these electromagnetic waves, existed and could potentially be harnessed for wireless signal transmission. Maxwell's work was purely theoretical.
• Heinrich Hertz (Proof of Wireless Transmission)
  • Achievement: Proved Maxwell's theory correct through experimentation.
  • Device: Created a device that allowed electrical sparks to leak between two steel balls.
  • Experiment: Placed a steel ball contraption (transmitter) connected to an electrical system at one end of a room and a similar system (receiver) at the other. When he tapped the transmitting ball, it sent wireless electrical impulses, and the receiving ball repeated the sequence by sending out sparks.
  • Significance: This "spark gap transmitter" was responsible for the first use of electromagnetic (radio) waves for transmission and reception, demonstrating wireless communication was possible.

Making Wireless Practical: Guglielmo Marconi

• Goal: To make wireless technology practical and usable for the public, moving beyond clunky equipment.
• Competition: Competed significantly with Nikola Tesla, who also sought to develop wireless technology.
• Innovations: Adapted Hertz's spark gap transmitter by replacing the receiving sparks with a small printer or inker, which recorded transmitted dots and dashes wirelessly. This innovation significantly eased the job of a wireless operator, who no longer had to manually interpret sounds, reducing mistakes.
• Key Achievements:
  • $\text{1897}$: Obtained a patent in England for the "wireless telegraph."
  • $\text{1897}$: Formed the Marconi Wireless Telegraph Company (later known as "British Marconi").
  • Expansion: Began installing wireless technology on British naval and private ships, then for his home country, Italy.
  • $\text{1899}$: Opened an American branch, commonly known as "American Marconi," due to success in Britain and Italy.
  • $\text{1901}$: Successfully sent wireless signals across the English Channel to a station in France.
  • $\text{1901}$: Later that same year, achieved a major breakthrough by successfully sending wireless signals across the Atlantic to the United States, utilizing strategically placed wireless buoys to relay the signal.

The Push for Voice and Key Inventions

• Lee DeForest (Pioneer of Voice Transmission)
  • $\text{1899}$: Wrote the first PhD dissertation on wireless technology.
  • $\text{1901}$: Challenged Marconi by attempting to cover the New York International Yacht Races for a rival news service.
    • Outcome: Both Marconi's and DeForest's signals jammed each other. This led to the discovery and critical understanding that "different frequencies" were necessary to prevent signal cancellation.
  • Advocacy: DeForest strongly advocated for voice transmission over Morse code (dots and dashes), which Marconi preferred.
  • Terminology Evolution: "Voice transmissions" were initially called "wireless telephony" but were later simplified to "radio," based on the use of radio waves for transmission.
  • Key Invention: The Audion (or Vacuum Tube):
    • Function: This essential device intercepted radio signals and greatly strengthened them, improving the clarity of dots and dashes, and eventually enabling clearer reception of voices and music.
    • Impact: The vacuum tube became the standard primary tool for radio for the next "$\text{40}$ years," marking a "huge electrical event" in communication.
• Reginald Fessenden (First Voice Transmission)
  • Background: Initially worked with Thomas Edison on radio concepts, then branched out to strengthen radio signals with various groups.
  • Invention: The Liquid Barretter: This invention was crucial as it permitted the first successful transmission and reception of human voice signals.
  • $\text{1906}$: Conducted the first public demonstration, transmitting a voice via airwaves from his station in Massachusetts with the help of GE.
    • Reaction: Ship operators in Massachusetts Bay, expecting Morse code, were initially surprised and thought it was a joke to hear an actual voice. This event was a major breakthrough that "the world was never the same."

The Evolution of