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Tutorial 3 – Tropospheric Ducting along the African Coasts
In today’s tutorial Mike Bosch ZS2FM focusses on Tropospheric Ducting
There are around 17 different modes of propagation present on VHF. Most of the strongest signals will appear on 50 MHz, the Magic Band. However, Tropo Ducting excels on the 144 MHz band where currently up to 5000 kilometres can be covered across the Pacific Ocean. Watch the Hepburn Forecasts on http://dxinfocentre.com/tropo.html for forecast on propagation Ducting conditions over the Atlantic and Indian Oceans south of the equator.
Propagation via Tropo Ducting exist along the West Coast of South Africa, Namibia, Angola, Zaire, Congo and Gabon, which is from the Equator and further down south. There are two islands well within the range of 3000 km from the African West Coast; they are St, Helena Island and Ascension Island. Currently V51PJ of Namibia and PY1MHZ in Brazil are conducting tests across the Atlantic on 144 MHz Digital.
On the other side of Africa there is the East Coast of South Africa, Mocambique, Tanzania and Kenya. There are several Islands within the range of 3000 km such as Madagascar, Reunion Island and Mauritius. Reunion Island has been worked from Port Elizabeth over a distance of 3245 km on 144 MHz Digital and from East London on 144 MHz SSB over a distance of 3000 km.
The greatest challenge that awaits amateurs on VHF is to bridge the Indian Ocean on 144 MHz with a two-way radio contact. The shortest distance between Australia and South Africa is around 8000 km between Perth and Port Elizabeth.
Next week we will discuss Sporadic-E propagation.
VHF, UHF AND A MICROWAVE NEWS
IN THE 1920’S AMATEURS WERE LICENCED ONLY AS RADIO EXPERIMENTERS – In the 1920’s amateurs were licenced only as radio experimenters, even in South Africa by the PMG. This was the time that amateur radio made its greatest contribution to radio science with the discovery of DX operation on shortwaves. In 1927 the ITU (then known as the International Radiotelegraph Union) at its Conference in Washington, allocated special bands to the five recognized services; Broadcasting, Martime Mobile, Fixed, Mobile and Amateur. The radio amateurs were rewarded with six amateur bands for their pioneering work on shortwaves.
As time passed so a new breed of radio amateurs started to change the face of amateur radio to that of a hobby where innovation and experimentation were no longer that important anymore. In modern times shortwave broadcasting and other commercial services started to desert the shortwave bands for greener pastures on satellites in the microwave spectrum where signals were more reliable and constant. Amateur Radio now has to play a catchup game if they wish to survive the 21st Century, bearing in mind that the modern generation is very computer literate and SDR would appeal to them, and they only need a type of amateur radio that is more attractive to them. Amateur Radio must make the necessary changes to meet future demands and become part of the new radio world again. Fortunately there are a number of dedicated amateurs in the USA and Germany who are doing some brilliant work on the amateur Microwave bands.
MICROWAVE UPDATE 2018 – An email arrived from Joe Burke, WA8OGS, asking us to help promote the above event. It will be hosted by the Midwest VHF/UHF Socxiety, and scheduled for 11 – 14 October 2018 at the Holiday Inn Dayton/Fairborn I-675. This is an international conference dedicated to microwave equipment design, construction and operation. Microwave Update is an ARRL technical conference, and ARRL publishes the conference proceedings. Some of the activities include Seminar Presentations, Antenna Gain Measurements, Door Prizes, Test and Measurement Lab, Flea Market, Banquet, Vendor Demo/Sales Area, Tour: Carillon Historical Park, Tour: Voice of America Museum, Tour: US Airforce Museum. Save the date, and make plans to attend, and help spread the word to others who might be interested.
NASA SCIENTISTS PREDICT THAT WE ARE NOW ENTERING THE MAUNDER MINIMUM WHERE THE GRAND MIMIMUM WILL OCCUR IN 2050 – The Sun has an 11-year cycle where it experiences minimum and maximum activity. Scientists say the Sun may soon experience its grand minimum phase. In this time, UV radiation diminishes beyond the lowest point of its cycle. Researchers have now developed a way to predict just how much the Sun will dim. The scientists say the Sun could become unusually cool as soon as 2050.
In the next 30 years, our Sun could dim significantly, leaving us with conditions that could create a mini ice age. That's according to new research from scientists who say they've figured out a way to track the Sun's 11-year cycle. It's commonly known that the Sun moves through an 11-year cycle where, similar to a heartbeat, it experiences active and quiet periods known as the solar maximum and solar minimum. Now, scientists from the University of California, San Diego, believe they've pinpointed exactly when the next solar minimum could occur, saying the Sun could become unusually cool as soon as 2050. The Sun could experience conditions last seen during the Maunder Minimum, an event in the mid-17th century when temperatures were low enough to freeze London's River Thames.
When the Sun experiences a solar maximum, the nuclear fusion at the Sun's core forces more magnetic loops to the surface, due to extreme ultraviolet wavelengths. Scientists have previously been able to predict when the next solar minimum will occur. In a solar minimum, the sun's magnetism diminishes, fewer sunspots form and less ultraviolet radiation makes it to the surface of the Sun. As a result, the sun's surface is clearer and it becomes dimmer.
But new data collected over the span of 20 years has helped the team of researchers determine just how much the Sun could dim during the 'grand minimum. During the grand minimum, the Sun is likely to be 7% cooler than the lowest point of its 11-year cycle, according to the scientists. When the Sun's energy is reduced, the first effect it will have on earth is a thinning of the stratospheric ozone layer. That thinning in turn changes the temperature structure of the stratosphere, which then changes the dynamics of the lower atmosphere, especially wind and weather patterns, the study notes. However, the cooling is not uniform. Again, the scientists refer to the Maunder Minimum, during which areas of Europe chilled significantly, but other areas such as Alaska and southern Greenland warmed.
You could just imagine what effect the Maunder Minimum could have on HF communications, when weak UV radiation can no longer ionize the F-layers properly.
Focus on VHF 11 Feb 2018
In today’s programme we focus on reports that the VHF path between Australia and South Africa is still the greatest challenge on 144 MHz and Trans equatorial propagation during the world wide SOTA weekend. But first our weekly tutorial
In our second tutorial we discuss the Ultra High Frequency bands commonly referred to as UHF. They cover the following frequency ranges
432 – 440 Megahertz and known as the 70 centimetre amateur band.
1240 – 1300 Megahertz or the 23 centimetre amateur band.
2320 – 2450 Megahertz or the 13 centimetre amateur band
The first two bands are quite popular in South Africa, whereas the latter is rarely used.
Tropospheric propagation modes such as Tropo Enhancement, Tropo Ducting and Tropo Scatter are still present on these bands. Tropo Ducting that appears when a temperature inversion is formed between 450 to 2000 metres above sea level in the atmosphere may present a skip distance where signals cannot be received, but it will conduct radio signals over long distances between two points. But if this duct occurs higher than 2000 metres then it could miss the Earth and signals would disappear into space.
So far only 432 Megahertz and 1296 Megahertz bands achieved communication over distances aroud 1000 km compared to distance of 5000 km possible on on the 144 Megahertz band across the Pacific Ocean via Tropo Ducting. The signal strength of radio signals on the UHF bands are normally weaker than those on the VHF bands. The Ultra High frequency bands require more sensitive receivers and higher gain Yagi beam antennas. Fortunately the UHF antennas are a much smaller and shorter than VHF antennas.
Tropo Scatter signals will be attenuated as the frequency rises, therefore the lower frequencies could be better for Tropo Scatter tests. With reference to the 13 centimetre amateur band the top band edge frequency of 2450 Megahertz is ued for microwave ovens.
Next week we will discuss propagation of Tropospheric Ducting along the African coast. Part 1 is now available on the SARL web Amateur Radio Today page. And now for today’s main stories:
The vhf path between Australia and South Africa is still the greatest challenge on 144 MHz – Many years ago the first attempt was made by Bill Hosie, VK6ACY (now ZS6CCY), near Perth and Mike Bosch ZS2FM in Port Elizabeth, assisted by Andre ZS2ACP and the late Jim Frans ZS2JF to establish a two-way contact across the Indian Ocean. Mike reports the team turns to transmit CW CQs for an hour or so daily on 144 MHz for a full month, separated by listening periods, without any success. “At that time we did not have the facility of the Hepburn Forecasts to predict Tropo Ducting across the Indian Ocean”’ Mike said
Many years later Keith Bainbridge, VK6RH, spokesman for the West Australian Radio Group tried to interest South African VHF amateurs to participate in their new chirp modulation tests, but the chirp equipment would come at a price. Unfortunately support was not forthcoming so a brilliant amateur radio science project just died.
Recently Andy Hemus at Carine, Western Australia tried to revive interest in a VHF path between VK and ZS. He says that if there is a VHF path from Eastern Australia to LU, VP8, CE etc, then here must be a VHF path between Western Australia and the East Coast of South Africa too. Who would like to take up the challenge?
Guru EA2IF is arranging a Trans-Equatorial Propagation (TEP) Sota Weekend for 6 ,10, 12 and 15 metre bands. Any mode is allowed. The events are planned around the equinoxes of 21 March and 21 September 2018. The first event is scheduled for Monday 19 March and ending on Sunday 25 March 2018. The ideal times for afternoon TEP will be from 15 to 19 hours local time. For VHF-UHF enthusiast and night activations there will be an opportunity to explore the evening TEP for which ideal times will be from 20 to 23 hours local time. There won’t be any problem with contacts made out of the mentioned bands and time window. This is not a contest with strict rules, so total freedom for anyone trying whatever they wish, as long as it respects the others and the country regulations. Read more on the SAL web. http://reflector.sota.org.uk/t/tep-trans-equatorial-propagation-worldwide-sota-week/16464
Peter ZS2ABF reports from East London about the coastal ducting on the night of 5th February. He, John ZS2AH, end Dave ZS5DJ had a great QSO that lasted for three quarters of an hour. QSB was again present, but generally conditions were very good. Signal strengths of 5-9 were received. Dave and Peter also switched over to the FM for a while, and due to the QSB they switched back to USB after a short QSO. At one stage Dave thought he could hear another very weak station trying to break in but due to the QSB the signals seemed to have disappeared.The following night Dave's signals never went above S-0. Dave heard Peter at S3 to 5 with QSB. Dave's Mast Head Pre-amp once again proved that it gave him a real advantage.
NASA’s 883 GHz ICE MAP – A bread loaf-sized satellite has produced the world’s first map of the global distribution of atmospheric ice in the 883 GHz band, an important frequency in the submillimetre wavelength for studying cloud ice and its effect on Earth’s climate. IceCube—the diminutive spacecraft that deployed from the International Space Station in May 2017—has demonstrated-in-space a commercial 883 GHz radiometer developed by Virginia Diodes Inc of Charlottesville. It is capable of measuring critical atmospheric cloud ice properties at altitudes between 5 and 15 km.
NASA scientists pioneered the use of submillimetre wavelength bands, which fall between the microwave and infrared on the electromagnetic spectrum, to sense ice clouds. However, until IceCube, these instruments had flown only aboard high-altitude research aircraft. This meant scientists could gather data only in areas over which the aircraft flew. According to scientists at NASA’s Goddard Space Centre, with IceCube scientists now have a working submillimetre radiometer system in space at a commercial price, and more importantly it provides a global view on Earth’s cloud-ice distribution.