Lecture Notes: The Great Seal Bug

Introduction

• Topic: The Great Seal Bug, a sophisticated Soviet listening device.
• Timeframe: Operated undetected from 1945 to 1952 at the US embassy in Moscow.
• Context: Presented as a gift by Soviet school children to the US ambassador.

Description of the Device

• Appearance: Hand-crafted wooden plaque of the Great Seal of the United States.
• Structure:
  • Metal cavity with a thin diaphragm acting as a microphone.
  • Small vibrating membrane.
  • Antenna designed to interact with radio waves.

Technical Specifications

• Size and Material:
  • Small copper cylinder.
  • Weighs approximately 31 g.
  • Measures 24 mm in length and 19 mm in diameter.
  • Interior polished with silver for enhanced signal reflection.
• Components:
  • Diaphragm: Thin metallic membrane.
  • Adjustable mushroom-shaped disc for capacitive coupling and reduced pneumatic damping.
  • Threaded tuning post for sensitivity and transmission adjustments.
  • Split fit brass cap and brass grill for securement and sound wave entry.
  • 22.8 cm long antenna for ultra-high frequency resonance (~1,700 MHz).

Functionality

• Transmission Method:
  • Unlike conventional bugs, it reflected external radio waves.
  • Soviets activated it remotely with high-frequency radio beams.
  • Frequencies similar to modern RFID systems between 800 MHz and 1.5 GHz.
• Process:
  1. Radio waves strike the antenna and enter the metal cavity.
  2. Diaphragm vibrates with speech, modulating the reflected waves.
  3. Modified waves return to Soviet surveillance van.
  4. High sensitivity receiver demodulates the signal back into sound.

Discovery and Impact

• Detection:
  • Detected accidentally by a British radio operator in 1952.
  • Alarm led to a deep sweep by American intelligence.
  • Found hidden in the Great Seal plaque.
• Significance:
  • Revolutionary passive design fooled traditional bug sweeping methods.
  • Prompted rapid development of advanced counter-surveillance technology.
  • Considered a Cold War masterpiece for its innovative approach.

Conclusion

• Legacy: Demonstrated the ingenuity of Soviet surveillance technology.
• Note: The Great Seal Bug required no power, wires, or complex circuitry, setting it apart from traditional espionage devices.

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(End of Lecture)