Submarine communications Extremely low frequency

1 submarine communications

1.1 explanation
1.2 difficulties of elf communication
1.3 ecological impact

submarine communications

the united states navy utilized extremely low frequencies (elfs) radio band , radio communications. submarine integrated antenna system (sias) research , development effort communicate submerged submarines. soviet/russian navy utilized elfs submarine communications system, zevs. indian navy has operational elf communication facility @ ins kattabomman naval base communicate arihant class , akula class submarines.

explanation

because of electrical conductivity, seawater shields submarines higher frequency radio waves, making radio communication submerged submarines @ ordinary frequencies impossible. signals in elf frequency range, however, can penetrate deeper. 2 factors limit usefulness of elf communications channels: low data transmission rate of few characters per minute and, lesser extent, one-way nature due impracticality of installing antenna of required size on submarine (the antenna needs of exceptional size in order achieve successful communication). generally, elf signals used order submarine rise shallow depth receive other form of communication.

difficulties of elf communication

one of difficulties posed when broadcasting in elf frequency range antenna size, because length of antenna must @ least substantial fraction of length of waves. put, 3 hz (cycle per second) signal have wavelength equal distance em waves travel through given medium in 1 third of second. taking account of refractive index, elf waves propagate slower speed of light in vacuum. used in military applications, wavelength 299,792 km (186,282 mi) per second divided 50–85 hz, equals around 3,500 6,000 km (2,200 3,700 mi) long. comparable earth s diameter of around 12,742 km (7,918 mi). because of huge size requirement, transmit internationally using elf frequencies, earth forms significant part of antenna, , extremely long leads necessary ground. various means, such electrical lengthening, used construct practical radio stations smaller sizes.

the maintained 2 sites, in chequamegon-nicolet national forest, wisconsin , in escanaba river state forest, michigan (originally named project sanguine, downsized , rechristened project elf prior construction), until dismantled, beginning in late september 2004. both sites used long power lines, so-called ground dipoles, leads. these leads in multiple strands ranging 22.5 45 kilometres (14.0 28.0 mi) long. because of inefficiency of method, considerable amounts of electrical power required operate system.

ecological impact

there have been concerns on possible ecological impact of elf signals. in 1984 federal judge halted construction, requiring more environmental , health studies. judgment overruled federal appeals court on basis navy claimed have spent on $25 million studying effects of electromagnetic fields, results indicating similar effect produced standard power distribution lines. judgment not accepted and, during time elf in use, wisconsin politicians such senators herb kohl, russ feingold , congressman dave obey called closure. similar concerns have, in past, been raised electromagnetic radiation , health.