TY  - RPRT
TI  - Letter Circular 614: radio transmission and the ionosphere (supersedes Letter Circular 575)
PY  - 1940
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 614
DO  - 10.6028/NBS.LCIRC.614
ER  -