TY  - RPRT
TI  - Letter Circular 567: methods of using standard frequencies broadcast by radio (replaces Letter Circular 498)
PY  - 1939
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 567
DO  - 10.6028/NBS.LCIRC.567
ER  -