TY  - RPRT
TI  - Letter Circular 578: sources of radio information (replaces Letter Circular 513)
PY  - 1939
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 578r1939
DO  - 10.6028/NBS.LCIRC.578r1939
ER  -