On Wed, 18 May 2005 20:18:34 -0700, Richard Clark
wrote:


I've been here too:
http://eyeball.sabotage.org/jcrs-eyeball.htm

Which is only 30 miles or so up the road. The last image, scroll
right, shows the bird's eye view, but it is impossible to make out the
cabling (that follows in the last link below, a big power point file).

NLK 24.8KHz 192/250KW

from
http://amrad.org/pipermail/lf/2001q2/001051.html
The antenna at Jim Creek (a U.S. Navy LF communications site).

The size of this station was a revelation to me. The antenna consisted of ten copperweld cables
8,000 feet long strung across a narrow valley between two ridges 3,000 feet high. The centers of
these strands were connected to downleads that were brought together into a sort of transmission
line that carried them back to the transmitter building. The antenna was actually separated into two
halves, each excited by its own transmitter, so that in case of accident or the need for maintenance
the station could operate at half-power for a time. The transmitter building was a concrete box a
hundred feet or so square without windows and with access to the area of the transmitter itself only
by elevator from below. As befitted a station with a transmitter whose component sections were
mostly of the order of cubes ten feet on a side, the elevator was so big that we simply drove our
truck into it for the ride up to the operating level,
We spent two or three days setting up our equipment and erecting a whip antenna for receiving the
signal from Criggion. As the transmitter building was the only possible site for our gear in the
immediate vicinity, the whip was installed on the roof about fifty feet from the "lead-in" which
carried about 700 amperes of radio-frequency current. It was in setting up this
antenna that we discovered the falsity of the common statement that "r.f. doesn't shock; it simply
produces surface burns". This may be the truth for small quantities as high-frequency currents tend
to flow only on the surface of a conductor, but it fails by a wide margin to explain the behavior of
large currents at such a low frequency as Jim Creek's. Our rough calibration of the field strength near
the transmitter lead-in was as follows: a bit of metal up to five or six inches long (such as a
screwdriver or a pair of pliers) stings like a nettle; rubber gloves are a necessity for handling metal
objects a foot or two long; and touching a conductor five or six feet long can knock one down.

There are various descriptions of antenna, frequency, and power that
is undoubtedly due to mission changes over the years. I've seen Jim
Creek specified at a frequency as low as 18KHz with powers ranging
from hundreds of KW to 1 MW. It is hard to tell if those
specifications are for driven power or radiated power as antenna
efficiencies are decidedly lucky to break 50%.

The most recent top hat design is illustrated at:
http://www.aavso.org/aavso/meetings/...esent/howe.ppt
which in a rough description is composed of 12 spans with 12 down
leads (bus fed); with the top hat dimension of one square mile. From
rough calculations, feedpoint R appears to be on the order of 2 Ohms.

73's
Richard Clark, KB7QHC

Here a similar (web)site for NAA:

http://web.elastic.org/~fche/mirrors...er-eyeball.htm

In the last image the shadows cast by the towers are easily visible.

I'm sure I've mentioned this before but our radio club once had a
speaker who was a Navy Reservist who did a summer tour at NAA. He had
a slide show that was really interesting.

Of particular interst to me was the fact that (at that time anyway)
the top hat was "spring loaded" and allowed to move about under
ice/wind loading. The "springs" were massive concrete block weights
that rode up and down inclined tracks on the outer ring of towers.

One other interesting thing was that when they used FSK, the antenna
was retuned between mark and space.