Digital transformation is fuelling weak signals communication

March 18th, 2019, Published in Articles: EngineerIT

Marconi may be the big name when talking about the development of radio at the beginning of the previous century, but several radio amateurs have made their mark in the history of communication. One of them is Joseph Taylor, a farm lad from Philadelphia in the USA who is today leading the digital transformation of amateur radio.

Joe K1JT, as he is known in the amateur radio world, developed digital communication modes that operate well below the noise. His latest development is FT8 which has captured the imagination of the amateur radio community. The new mode is named after its developers, Steven Franke (K9AN) and Joe Taylor (K1JT). The numeral designates the mode’s eight-frequency shift keying format.

Born to experiment

Joe Taylor in his radio room

Joe Taylor was born to experiment. He was awarded the Nobel Prize in physics in 1993 for the discovery of a binary pulsar, a discovery which has opened up new possibilities for the study of gravitation. In his acceptance speech, he talked about his early boyhood days where the direction for his career path developed. He told the learned audience at the Nobel Prize ceremony that among his fondest memories is, together with his brother Hal, erecting numerous large rotating ham-radio antennas high above the roof of their three-story Victorian farmhouse. “With one such project we managed to shear off the brick chimney, flush with the roof, much to the consternation of our parents.”

That incident was one of many practical lessons of his youth, often involving ill-advised shortcuts toward some goal. In their school years, the two brothers filled most of the third floor of their farmhouse with working ham-radio transmitters and receivers. Their rigs were mostly built from a mixture of post-war surplus equipment and junk television sets. They learned by experience that when high-voltage was needed, the power company’s 6000-to-120-volt transformers work admirably in reverse; and most amplifiers will oscillate, especially if that is not what was wanted.

More recently, addressing an ITU conference, he said: “New discoveries that have fundamentally changed or expanded our understanding of nature’s laws, or might do so in the near future will not affect the communication’s world for many decades to come. This is because our fundamental understanding of electromagnetism is already in a mature state. Maxwell’s equations which have been thoroughly tested for the past 150 years in principle tell us everything we need to know in order to exploit the wonders of telecommunications at the speed of light. Our understanding of these laws of nature, including what they tell us is possible and not possible, is not likely to change. But of course, we can still develop new and improved ways of generating, controlling and detecting electromagnetic radiation, as well as clever new ways of effectively sharing the spectral resources that we have. The fundamental science may be mature, but technology’s ability to exploit and build upon electromagnetic phenomena is still rapidly developing.”

Limitations of the radio spectrum are a result of fundamental laws of nature. Every nation on Earth have, in principle, access to the same spectrum as everyone else. The amount of accessible oil, on the other hand, depends on the much more complicated way the earth formed and evolved over time. These fuels are not evenly distributed over the earth and they are expendable. When it’s gone, there’s none left. The electromagnetic spectrum, on the other hand, will always be there, whether or not we humans are around. Moreover, the spectrum can be shared by many users simultaneously, and shared use can be especially effective if adequate planning is done in advance.

“Future technologies will surely make even better uses of wireless communication than we do today. I foresee plenty of scope for contributions for new technologies. Information and communication technologies have much to offer for the betterment of the human condition everywhere, and perhaps especially so in the developing world. It is extremely important to continue seeking the best efficiencies in the use of the spectrum.”

The FT8 protocol

Fig. 1: Typical screenshot of WSJT-X.

FT8 is a new protocol that comes out of the original WSJT development, a computer program used for weak-signal radio communication. The WSJT program is now open source with continual development by a small team. The digital signal processing techniques in WSJT make it substantially easier for radio amateurs to employ esoteric propagation modes, such as high-speed meteor scatter and moon-bounce.

The software carries a general emphasis on weak-signal operation and advanced digital signal processing (DSP) techniques; however, the communication modes rely upon different ionospheric propagation modes and may be used on many different frequency bands.

WSJT’s communication modes can be divided into fast and slow modes. While fast modes send character-by-character without error correction, the slow modes aim to optimise for minimal QRO (high-power) use.

JT65, developed and released in late 2003, is intended for extremely weak but slowly varying signals, such as those found on tropospheric scatter or Earth-Moon paths. It can decode signals many decibels below the noise floor in a 2500 Hz band and can often allow amateurs to successfully exchange contact information without signals being audible to the human ear. Like the other modes, multiple-frequency shift keying is employed but unlike the other modes, messages are transmitted as atomic units after being compressed and then encoded with a process known as forward error correction (FEC). The FEC adds redundancy to the data, such that all of a message may be successfully recovered even if some bits are not received by the receiver.  Because of this FEC process, messages are either decoded correctly or not decoded at all, with very high probability. After messages are encoded, they are transmitted using MFSK with 65 tones.

Radio amateurs have also begun using the JT65 mode for contacts on the HF bands, often using QRP (very low transmit power). While the mode was not originally intended for such use, its popularity has resulted in several new features being added to WSJT in order to facilitate HF operation.

Compared to the so-called “slow modes” (JT9, JT65, QRA64), FT8 is a few decibels less sensitive, but allows completion of two-way contacts four times faster. Compared with the “fast modes” (JT9E-H), FT8 is significantly more sensitive, has much narrower bandwidth, uses the vertical waterfall, and offers multi-decoding over the full displayed passband. Features not yet implemented include signal subtraction, two-pass decoding, and use of already known information as it accumulates during a contact.

No doubt Taylor and his team will continue to develop new techniques, as he so often says “this is only the beginning”.

Will this digital transformation mean the end of traditional amateur radio where the microphone and the Morse key were the main focus? Definitely not! But what is certain, here too digitisation will also have an impact as already seen in DStar and DRM replacing analogue audio with digital audio.

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