A Chinese antenna sends very low frequency radio waves to Earth

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  • The location of the antenna has not been revealed, but its signals can reach submarines over great distances, the researchers said.
  • A joint experiment with Russia has confirmed that a “ping” of the installation can also effectively travel underground.

The largest antenna on the planet is in operation in central China, opening up long-distance communications with submarines as well as civilian applications, according to engineers and scientists involved in the project.

The exact location of the facility has not been revealed, but it is believed to be somewhere in the Dabie Mountains, a protected nature reserve straddling Hubei, Anhui and Henan provinces.

From space, the antenna, which is formed from a network of cables and pylons similar to those of ordinary power lines, would look like a giant cross more than 100 km (62 miles) long and wide.

But at the ends of these lines, copper knots are set deep in thick granite. Two powerful underground transmitters – able to operate independently in case one is damaged – charge a megawatt of electric current and turn the Earth into a giant radio station.

According to an article published last month in the Chinese Journal of Ship Research, receiving devices planted 200 meters (700 feet) below the surface of the seabed can effortlessly pick up signals from the giant antenna 1,300 km (800 miles) – a range that covers the Korean Peninsula, Japan, Taiwan and the South China Sea.

The project’s lead engineer, Zha Ming, and his colleagues, from the Wuhan Maritime Communications Research Institute, said the facility was designed to maintain underwater communications for a total distance of 3,000 km. (1,900 miles) – enough to reach Guam, the largest US military base in the western Pacific Ocean.

The very low frequency (ELF) installation can generate electromagnetic waves from 0.1 to 300 Hz. These radio waves can travel great distances underwater and underground.

But the challenge was to distinguish the man-made signal from the natural low-frequency background noise.

China has also conducted a joint experiment with Russia to see how far the signal can travel through the ground. A Russian station received the ping at 7,000 km (4,400 miles), but the increased distance came at a cost – communication was one-way and could only send encrypted text messages.

But Chinese military researchers have said submarines and smart devices, such as underwater drones, could receive an order – or a target – and act quickly while remaining stealthy.

An ELF signal is difficult to generate because its wave may be wider than a continent. A conventional radio tower would need to be at least 1,000 km (600 miles) high to do the job.

The idea of ​​building a land-based low-frequency antenna dates back to the 1960s. The US Navy’s Project Sanguine, for example, envisioned an antenna covering more than two-fifths of Wisconsin to command submarines around the world.

An antenna with two crossover lines, each about 70 km (40 miles) long, was eventually built and began generating signals at a frequency of 76 Hz from the late 1980s.

The project ended in 2005, after failing to meet Army expectations. The United States has turned to alternative technologies, such as manipulating the atmosphere with lasers to generate low-frequency waves.

Building an ELF antenna to meet the changing demands of real-world applications posed many challenges, according to Zha and his colleagues.

Powerful electric currents, for example, could generate a strong magnetic field that would reduce the conductivity of the cables.

To ensure that messages can be received and read over long distances, radio waves must be precisely tuned by hundreds of advanced electronic devices. But their stability could be severely affected by the intense electromagnetic field produced by the giant transmitters.

The Chinese team said it had developed effective measures to address these issues, with test results suggesting that the performance of the facility had met or exceeded all design criteria.

Although the researchers did not directly reveal the location of the facility, they did provide its relative distance to a number of Chinese cities – approximately 1,000 km south of Beijing, 2,000 km south- east of Dunhuang in northwestern China and 1,000 km east of Mianyang in southwestern province. from Sichuan – placing it somewhere in the Dabie Mountains.

The Chinese antenna is the world’s first large-scale ELF facility open to non-military users, according to the research team.

It has been used in a number of geological studies in search of untapped mineral or fossil fuel reserves, particularly those buried thousands of meters underground and overlooked by conventional detection methods.

Scientists are also using the signals to monitor active fault lines and calculate earthquake risks for major Chinese cities.

The health effects of ELF waves have been debated for decades. While some studies of residents living near high voltage power lines have suggested an increased risk of cancer and other diseases, other studies have produced different results.

Some lab experiments have found evidence that living under intense exposure to low-frequency radio waves can damage animal organs.

A study in August by medical researchers from Shanghai Jiao Tong University confirmed that a day’s exposure to a 50 Hz electromagnetic field could alter the expression of certain genes in mice and affect growth. neuronal fibers.

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