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
Transceiver direct conversion, short-wave, all-band. QRPver Minion Mini DC-3001 This is a small-size multi-band short-wave QRP transceiver. The transceiver is built according to the transceiver scheme with direct frequency conversion. The d... Read more
ncrease your station’s receive performance with new book Receiving Antennas for the Radio Amateur by ARRL author Eric P. Nichols, KL7AJ. Although the fundamental characteristics of antennas apply to both transmission and reception, t... Read more
The results are in, and more than 90 submitted entries for the November 3 running of the Frequency Measuring Test (FMT). Thirty stations were able to... Read more
DESIGN & BUILD A SINGLE-SIDEBAND TRANSCEIVER FROM SCRATCH PART 1 Read Full Article: Read more