Page 29 - EngineerIt January 2021

AMATEUR RADIO

The FT8 protocol Moon paths. It can decode signals many decibels below the noise floor in a 2500 Hz band
FT8 is a new protocol that comes out of the and can often allow amateurs to successfully exchange contact information without signals
original WSJT development, a computer being audible to the human ear. Like the other modes, multiple frequency shift keying is
program used for weak signal radio employed but unlike the other modes, messages are transmitted as atomic units after
communication. The WSJT program is now being compressed and then encoded with a process known as forward error correction
open-source with continual development by (FEC). The FEC adds redundancy to the data, such that all of a message may be
a small team. The digital signal processing successfully recovered even if some bits are not received by the receiver. Because of this
techniques in WSJT make it substantially FEC process, messages are either decoded correctly or not decoded at all, with very high
easier for radio amateurs to employ probability. After messages are encoded, they are transmitted using MFSK with 65 tones.
esoteric propagation modes, such as high Radio amateurs have also begun using the JT65 mode for communication on the HF
speed meteor scatter and moon-bounce. bands, often using QRP (very low transmit power). While the mode was not originally
The software carries a general emphasis intended for such use, its popularity has resulted in several new features being added to
on weak signal operation and advanced WSJT to facilitate HF operation.
digital signal processing (DSP) techniques; Compared to the so-called “slow modes” (JT9, JT65, QRA64), FT8 is a few decibels
however, the communication modes rely less sensitive, but allows completion of two-way contacts four times faster. Compared with
upon different ionospheric propagation the “fast modes” (JT9E-H), FT8 is significantly more sensitive, has much narrower
modes and may be used on many different bandwidth, uses the vertical waterfall, and offers multi-decoding over the full displayed
frequency bands. passband. No doubt Taylor and his team will continue to develop new techniques; as he so
WSJT’s communication modes can often says, “this is only the beginning”. Details of the various weak signal modes can be
be divided into fast and slow modes. found at https://physics.princeton.edu/pulsar/k1jt/
While fast modes send character-by-
character without error correction, the But is all this digital stuff amateur radio?
slow modes aim to optimise for minimal This is a question often asked. If it is linked back to the ITU definition, being: “A radio
QRO (high-power) use. communication service for the purpose of self-training, inter-communication and technical
JT65, developed and released in late investigations carried out by amateurs, that is, by duly authorised persons interested in
2003, is intended for extremely weak but radio technique solely with a personal aim and without pecuniary interest”, the answer is a
slowly varying signals, such as those definite yes. However, this does not mean that the amateur radio analogue is now
found on tropospheric scatter or Earth- something of the past. It will still be around for a long time. n

Fundamental understanding of electro-magnetism is mature

More recently, addressing an ITU conference, Joe Taylor said: Moreover, the spectrum can be shared by many users
“New discoveries that have fundamentally changed or simultaneously, and shared use can be especially effective if
expanded our understanding of nature’s laws, or might do so in adequate planning is done in advance.
the near future, will not affect the communications world for “Future technologies will surely make even better uses of
many decades to come. This is because our fundamental wireless communication than we do today. I foresee plenty of scope
understanding of electro-magnetism is already in a mature for contributions for new technologies. Information and
state. Maxwell’s equations which have been thoroughly tested communication technologies have much to offer for the betterment
for the past 150 years in principle tell us everything we need to of the human condition everywhere, and perhaps especially so in
know in order to exploit the wonders of telecommunications at the developing world. It is extremely important to continue seeking
the speed of light. Our understanding of these laws of nature, the best efficiencies in the use of the spectrum.” n
including what they tell us is possible and not possible, is not
likely to change. But of course, we can still develop new and Joe Taylor K1JY
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 electro-magnetic phenomena is still
rapidly developing.”
Limitations of the radio spectrum are a result of
fundamental laws of nature. Every nation on Earth has, 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 electro-magnetic spectrum, on the other hand, will
always be there, whether or not we humans are around.

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