commgrp@silver.bacs.indiana.edu (BACS Data Communications Group) (03/14/88)
posted to rec.ham-radio and sci.electronics:
From ELECTRONICS & WIRELESS WORLD (British electronics magazine),
January 1986, p. 63:
"...Since the experiments...by RCA in 1966-67 when it was shown that
worldwide communications was feasible on frequencies below 100Hz,
there has been growing interest in... the ELF band of 3 to 3000 Hz...
"Project Sanguine" of the Lincoln Laboratory... maximum radiated power
was not more than 0.5W at 45Hz, 1W at 75Hz but decodable signals were
received in Norway, Malta, Saipan and Hawaii using modest air-core
loop receiving antennas. Attenuation of signals can be as low as
1.5dB over 1000km... The U.S. Navy has an ELF station in Wisconsin on
76Hz...for reception by submarines.
"...It is possible to use the Earth's atmosphere as an antenna, for
example by modulating the conductivity of the polar electrojet.
As reported in _Nature_ (Sept. 12, 1985), this has been achieved
experimentally by operating the high-power ionospheric heating
transmitter (270 megawatts on 2.759MHz) at Ramfjord, near Tromso in
Northern Norway, sinewave modulated at 1.57kHz or 1.04kHz.
"As a result of the ionospheric non-linearity this resulted in
variable RF output at 1.57 or 1.05kHz ranging from under 100
microwatts to over 2 watts radiated from the electrojet and
successfully received at test sites 205 and 554km from Ramfjord with
attenuation of between 5 to 30dB/1000km.
"...Increasing the electron temperature of the ionospheric layers to
permit extended range of VHF signals by field-aligned scatter
techniques has led to the development of high-power ionospheric heater
transmitters. Whether their use can be extended to practical ELF
systems remains to be seen."
--------
Where are other "ionospheric heaters" located? How large are their
areas of influence? Are their VHF effects useful at ham-radio power
levels? Are their operating schedules available? Can NSA sneak
things like that past the environmentalists? :-)
What is the polar electrojet?? I assume it's related to the effect
associated with aurora, where charged particles in space are funneled
toward the earth at the magnetic poles.
It takes megawatts and tens of miles of antenna to make 1 watt ERP at
<100 Hz; this might be a good application for superconductors. The
Clam Lake, WI site of the Navy's ELF transmitter (strongly opposed by
environmentalists but now in operation) was supposedly chosen because
of desirable electrical properties of the granite bedrock there.
Perhaps there are advantages to having it in the vicinity of the north
magnetic pole (which is somewhere in the Hudson's Bay region).
I'm interested in VLF and ELF for underground communication ("cave
radio"). What kind of recievers are used for ELF? (_The Hunt for Red
October_ mentions ELF but provides no details other than the extremely
low data rate.) I surmise that submarines use sophisticated
correlation methods, perhaps synchronized by on-board atomic clocks.
Have amateurs detected the Navy's 76Hz signal? Do the Soviets have an
ELF system?
--
Frank W9MKV @ WA8YVR
reid@gold.bacs.indiana.edu
reid@iubacs.bitnet