817921

Information

• Patent Grant
• 817921

• References
• Source

• Patent Number

  817,921

• Date Filed

  Not available

• Date Issued

  Tuesday, April 17, 1906
  118 years ago

• CPC

  • H04B1/582 - with automatic balancing
  • H04M3/2281 - Call monitoring

• US Classifications

  • 379 - Telephonic communications