A fundamentally new approach to building radio transmitters could open previously impossible communication channels for warfighters
Here’s something easy to forget when you are chatting on your cell phone or flipping channels on your smart TV: although wireless communication seems nothing short of magic, it is a brilliant, reality-anchored application of physics and engineering in which radio signals travel from a transmitter to a receiver in the form of electric and magnetic fields woven into fast-as-light electromagnetic waves. That very same physics imposes some strict limits, including ones that frustrate the Department of Defense. Key among these is that radio frequency signals hit veritable and literal walls when they encounter materials like water, soil, and stone, which can block or otherwise ruin those radio signals. This is why scuba buddies rely on sign language and there are radio-dead zones inside tunnels and caves.
With his newly announced A Mechanically Based Antenna (AMEBA) effort, program manager Troy Olsson of DARPA’s Microsystems Technology Office is betting on a little-exploited aspect of electromagnetic physics that could expand wireless communication and data transfer into undersea, underground, and other settings where such capabilities essentially have been absent. The basis for these potential new abilities are ultra-low-frequency (ULF) electromagnetic waves, ones between hundreds of hertz and 3 kilohertz (KHz), which can penetrate some distance into media like water, soil, rock, metal, and building materials. A nearby band of very-low-frequency (VLF) signals (3 KHz to 30 KHz) opens additional communications possibilities because for these wavelengths the atmospheric corridor between the Earth’s surface and the ionosphere—the highest and electric-charge-rich portion of the upper atmosphere—behaves like a radio waveguide in which the signals can propagate halfway around the planet.
“If we are successful, scuba divers would be able to use a ULF channel for low bit-rate communications, like text messages, to communicate with each other or with nearby submarines, ships, relay buoys, UAVs, and ground-based assets, Through-ground communication with people in deep bunkers, mines, or caves could also become possible,” Olsson said. And because of that atmospheric waveguide effect, VLF systems might ultimately enable direct soldier-to-soldier text and voice communication across continents and oceans.
To date, there’s been a huge and expensive rub to actually pulling off low-frequency radio communication in the versatile ways that Olsson has in mind. The wavelengths of VLF and ULF radio signals rival the distances across cities and states, respectively. And since longer wavelengths have required taller antennas, communications in these frequency bands have entailed the construction of enormous and costly transmitter structures. A VLF antenna that the Navy built on a remote peninsula in Cutler, Maine, in the heat of the Cold War just to send a trickle of data to submarines makes the point: the gargantuan transmitter complex occupies 2,000 acres, features 26 towers up to 1,000 feet high, and operates with megawatt levels of power….READ MORE
HF/6m linear amplifier 2400W MRF1K50H 2 pcs water cooling system 5″ LCD touch screen for N0JSN Read more
“The Legendary G5RV Antenna” is the topic of the new (August 15) episode of the ARRL The Doctor is In podcast. Listen…and learn! Read more
Amateur Electronic Supply (AES) has announced that it is ceasing operations as of the end of July, 2016. The Milwaukee-based retailer has four locatio... Read more
ARRL is rolling back Outgoing QSL Bureau rates to 2011 levels. Effective May 15, 2019, the new rates will be: $2 for 10 or fewer cards in one envelope... Read more