ELF Propagation Study (Phase 1 - Summer 1970)

Abstract : With the availability of an ELF transmitter (the Bravo test facility at Clam Lake, Wisconsin) it now becomes feasible to make far-field field strength measurements at the lower ELF frequencies. Field strength measurements were made in Hawaii and California at 45 and 75 Hz in an attempt to determine the east-west attenuation rate under daytime or nighttime conditions over the propagation path. As a result of high atmospheric noise conditions and a low transmitted power level, the relatively large uncertainty in signal estimates makes accurate estimation of alpha impossible. However, the data indicate a daytime east to west attenuation rate between 0.7 and 1.2 db/Mm and a nighttime rate between 1.0 and 1.8 db/Mm. Future experiments are being planned to refine the estimates of alpha to within plus or minus 0.2 db/Mm. (Author)