SA radio amateurs face frequency challenge

April 17th, 2013, Published in Articles: EngineerIT

by Hans van Groenendaal, features editor, EngineerIT

In this monthly feature, Hans van de Groenendaal ZS6AKV, executive chairman of the South African Amateur Radio Development Trust (SAARDT), looks at various technologies and activities that drive amateur radio. SAARDT is dedicated to the development of amateur radio in South Africa with a special interest in the youth. The organisation is funded by donations and supports the South African Radio League and SA AMSAT.

Rassie Erasmus, SARL president at
his amateur radio station, ready to test
on the 5 MHz frequency.

The Independent Communications Authority of South Africa (ICASA) has issued licences for experimentation on three new frequencies, 5250, 5260 and 472 kHz to the South African Radio League (SARL).

The SARL has for many years been petitioning ICASA to allocate frequencies in the 5 MHz band for propagation research. The efforts to persuade ICASA intensified after the 2012 World Radio Conference (WRC12) when an agenda item for a new amateur allocation around 5 MHz was accepted for the WRC15 conference.

Agenda item 1.4 focuses primarily on using the proposed allocation for emergency communications. The resolution noted that “communications in the HF bands that are allocated to the amateur service play a major role in work to mitigate catastrophes and in the delivery of communications in support of relief operations in areas where the telecommunication infrastructure is weak or has collapsed,” and that “radiocommunication in the HF bands is dependent on propagation factors, with the result that frequencies in different bands have to be used to maintain stable communication for a relatively sustained period of time, with frequency changes in the case of communications with different correspondents located at very different distances.” The band 5250 – 5450 kHz is allocated to the fixed and mobile services, except aeronautical mobile, on a primary basis. The proposal maintains that “an allocation of an appropriate amount of spectrum, not necessarily contiguous, to the amateur service at around 5300 kHz would be adequate to better satisfy its needs associated with use for providing communications in disaster situations and during relief operations.”

ICASA has issued the SARL with two licences, 5250 and 5260 kHz, for a period of eight months to carry out propagation studies. After the initial period there is an opportunity to apply for a further period of eight months. This in contrast to regulators in many other countries who have made spectrum available free of charge for longer periods, in some instances till the WRC 15 conference.

While the propagation of signals are fairly well known for high power broadcasting, there is still quite a lot that can be learned by radio amateurs, especially on “inland” work, away from the coastline.

Previous propagation research carried out on the Cape south coast seawards of Mosselbay in the late afternoon and early evenings showed that 5 MHz will provide E-layer propagation for about an hour or two. This also occurred “up and down” the Outeniqua coastline.

Propagation modelling shows that the E-layer at those times is between 110 and 80 km above the Earth, much lower than the F layer. As the signal path was much shorter, very strong signals could be obtained with relatively low effective radiated power (ERP).

“It would be interesting to see how far and wide this propagation mode does actually occur in South Africa,” said SARL president Rassie Erasmus ZS1YT, commenting on the new licences. “I believe that radio amateurs can play a major role as they are not constrained by operational requirements and business financial constraints.”

The current problem with the amateur allocations at 40 and 80 m is that the two bands are an octave apart in frequency. At certain times the maximum usable frequency (MUF) falls below 7 MHz in the 300 to 500 km distance range, the lowest usable frequency is still above 4 MHz. This is especially true in the late afternoon/early evening. This leaves radio amateurs without a direct workable HF frequency over these moderate distances. When the MUF falls below 7 MHz, the lower portion of 5 MHz is perfect in the optimum traffic frequency (OTF) range that then stretches from about 4,9 to 5,6 MHz.

The frequency 5260 kHz will be made available to SARL members who register with the organisation for communication with other registered amateurs. This frequency was chosen as it was the most common frequency allocated in other countries and will afford international research. “We expect radio amateurs to keep detailed logs of their communication so that we may collect as much data as possible,” said Erasmus. “The frequency 5250 kHz will be used for more formal research between various parts of the country. We are also looking a possible automatic beacon operation.”

Details of the SARL 5 MHz project activity can be found on:
www.amateurradio.org.za/5MHz.htm

Back on medium wave

At WRC 12, radio amateurs were given access to 472 kHz, the frequency range that was used by the early amateurs when radio first became a reality. While ICASA follows the outcome of the decisions taken at the ITU WRCs, the process to get it gazetted is a cumbersome process and takes a long time. To catch the enthusiasm for the historical frequency, the SARL followed a similar process as for 5MHz and was granted a pilot licence for eight months. The SARL hopes that before the eight months are over ICASA will have completed the gazetting process and that the allocation is included in the national table of frequency allocations. According to ICASA the draft document is currently with the Department of Communication for ratification.

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