Page 25 - EngineerIt March 2021

LEGAL OPINION AMATEUR RADIO

Beacon programme to study inland

tropo in South Africa

At the annual HamSCI workshop held on the Zoom platform on 19 March 2021, Brian Jacobs and
Hans van de Groenendaal presented a paper on the South African beacon programme to study

propagation on VHF to a worldwide audience. The paper was presented during an Iposter session
which is itself an interesting way of presenting a paper.

Inland tropospheric propagation
Spectacular tropospheric ducting occurs regularly along the coasts of South Africa and
is especially strong and regular on the west coast of South Africa and Namibia where
the cold Benguela current off the south Atlantic plays a major role. Radio communication
between South Africa and St Helena Island occur regularly.
Tropospheric propagation over the oceans is well documented and has been the
subject of several studies. There are also good prediction models available, such as the
Hepburn Charts; these are fairly accurate and updated frequently.
The question is often asked whether tropospheric propagation can only happen in
coastal areas. While some sporadic tropospheric conditions inland have resulted in long
distance two metre contacts, they mostly occurred by accident; someone just happened to
be on the air. These reports confirm that it can happen inland but how frequently and what
type of tropospheric propagation remains unanswered.
VHF and UHF radio propagation remains a mystery Brian Jacobs ZS6YZ SARL
Most amateurs believe that the frequencies in the VHF and above bands (frequencies Beacon Manager
above 30 MHz) are only used for FM repeater operations. This is a misconception as
very good distances can be achieved using simplex and digital modes. Having beacons
to monitor will help gather the data that we need to better understand VHF propagation SARL beacon project
and under what conditions we can achieve those really long distance contacts. We The SARL beacon project was born
also believe that as we deploy more beacons and develop a better understanding of out of an idea suggested during a
tropospheric propagation, more radio amateurs will become active on the VHF and VHF workshop in October 2018 at the
above bands. National Amateur Radio Centre. At this
The enquiring nature of radio amateurs has, over many years, resulted in informal workshop it was decided to form a VHF
research, with the setting up of beacons and monitoring signals. But this hand-to-mouth work group to drive the development of
way of doing things has not really delivered the kind of data that enables meaningful and a beacon in the centre of the country
scientific findings. All it really shows is that long distance communication of frequencies to study the propagation path between
above 30 MHz is possible and does regularly occur. Cape Town and Gauteng, which are the
No one is in front of a radio 24/7, so many band openings will go unnoticed. There two centres of VHF and above activity in
are tools that can be used to tell you when and where the bands are open, but in order to the country. In December 2019, the test
know when the band is open, someone must transmit a signal and someone else must beacon ZS0BET went live from a location
receive that signal and report that the signal has been received. overlooking Bethlehem. This beacon
Therefore, beacons are so important because they continuously send out a signal 24/7 was a modified commercial ICOM radio
and you can listen for them and when received, you know which path is open and how transmitting a CW signal by way of keying
strong the opening is. the power amplifier stage. This beacon
Beacons are a method to monitor propagation on the VHF and above bands. Properly has been performing very well and
coordinated omni-directional beacons that follow the IARU recommendations will make it reception reports have come in from some
easier to monitor them electronically, allowing us to continuously collect data that can be unexpected areas. These unexpected
used to analyse how the propagation changes over time, for example as weather patterns reception reports have fuelled the quest
move across the country. At the same time, having this information readily available will to understand more about tropospheric
enable one to quickly get on air to exploit the propagation openings as they occur. propagation, especially inland.

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