TY  - RPRT
TI  - Mode calculations for VLF propagation in the earth-ionosphere waveguide 
AU  - Spies, Kenneth P
PY  - 1961
PB  - National Bureau of Standards
CY  - Gaithersburg, MD
SN  - NBS TN 114
DO  - 10.6028/NBS.TN.114
ER  -