Text 66750, 67 rader
Skriven 2011-10-15 08:43:00 av TOM WALKER (1:123/140)
     Kommentar till en text av ED VANCE
Ärende: SK ?
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EV>TW>As a side note the west Coast transmiter site up in Washington State
EV>TW>runs 1,200,000 Watt Transmitter.
EV>TW>That have an equilivent site on the East Coast and lower powered
EV>TW>stations world wide.
EV>TW>They operate in the VLF frequency band which is the 3Hz top 30Hz

As Agust pointed out by August Typo Tom meant KHz for the VLF frequency
band. :-)

EV>I would have thought the Navy would had put their west coast
EV>transmitter futher South, say like somewhere in California, instead of
EV>way up North in Washington State, so Subs in the South Pacific Ocean
EV>would receive a decent signal, but I suppose with over one Million Watts
EV>that west coast transmitter probably could be heard by Submarines in the
EV>Atlantic Ocean also.   ;-)

The consideration of the Transmitter sites involved the distance to
the Target. They are Al in the Notheren Hemisphere.The Poliris Missle
Subs in the Pacific were based in Guam. But with the Trident Subs and
their Extended Missle range they were stationed in Bangor Washington.
IInm both cases the targets cen be reached form a submerged submarine
just off the their base. In fact the Puget Sound inlet is so deep they
only have to be several hundered yards off the Pier.
In the 80's the Navy experiemnented with ELF frequencies and built a
Transmitting site up in Wisconson. It worked but had soem disantavges so
the project was dismantled i n2004.
Here is a small intersting bit from the interent.

***

Because of the electrical conductivity of seawater, submarines are
shielded from most electromagnetic communications. Signals in the ELF
frequency range(3 Hz to 30KHz), however, can penetrate much deeper. Two
factors limit the usefulness of ELF communications channels: the low
data transmission rate of a few characters per minute and, to a lesser
extent, the one-way nature due to the impracticality of
installing an antenna of the required size on a submarine (antennas need
to be of exceptional size for the users to achieve successful
communication). Generally, ELF signals were used to order a submarine to
rise to a shallow depth where it could receive some other form of
communication.

One of the difficulties posed when broadcasting in the ELF frequency
range is antenna size. This is because the antenna must be at least a
substantial fraction of the size (in at least one dimension) of the
wavelength of the frequency of the EM waves.
For ELF, this is very slightly slower than the speed of light in a
vacuum. As used in military applications, the wavelength is ~186,282
mi per second divided by 50-85 Hz, which equals around 2,192 to
3,726 mi long; by comparison, Earth's diameter is around 7,918 mi.
Because of this huge size requirement and, to transmit internationally
using ELF frequencies, the earth itself must be used as the antenna,
with extremely long leads going into the ground.

The US maintained two sites, in the Chequamegon-Nicolet National Forest,
Wisconsin and the Escanaba River State Forest, Michigan (originally
named Project Sanguine, then downsized and rechristened Project ELF
prior to construction), until they were dismantled, beginning in late
September 2004. Both sites used long power lines, so-called ground
dipoles, as leads. These leads were in multiple strands ranging from
22.5 to 45 kilometres (14.0 to 28 mi) long. Because of the inefficiency
of this method, considerable amounts of electrical power were required
to operate the system.

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