@misc{1173436,
  author = {HJ Walls},
  title = {Letter Circular 92::radio signals of standard frequency and their utilization},
  year = {1923},
  month = {1923-01-01 05:01:00},
  publisher = {, National Institute of Standards and Technology, Gaithersburg, MD},
  doi = {https://doi.org/10.6028/NBS.LCIRC.92},
  language = {en},
}