SA radio amateurs seek allocation around 5 MHz

July 24th, 2012, 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.

For emergency communication such as services offered by the South African Radio League HAMNET, it is important that high frequency (HF) coverage is available at all times. This is currently not possible with the frequencies available to radio amateurs. The allocations at 40 and 80 m are an octave apart in frequency which means that there are periods in the late afternoon and early evening when no communication is possible over a distance between 300 – 500 km.

When the maximum usable frequency (MUF) falls below 7 MHz in the 300 to
500 km distance range, the lowest usable frequency (LUF) is still above 4 MHz. This is especially true in the late afternoon and 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 range that then stretches from about 4,9 to 5,6 MHz.

The problem is not limited to South Africa and has resulted in the International Amateur Radio Union lobbying the International Telecommunications Union to have a permanent allocation in the 5 MHz band for radio amateurs. Until the World Radio Conference 2012 held in January, these efforts did not find favour, but all changed when Cuba submitted a proposal during the final plenary that the allocation on an amateur allocation at 5 MHz be placed on the WRC15 conference agenda.

Now known as Agenda Item 1.4, it focuses primarily on using the proposed allocation for emergency communications. The resolution noted “communications in the HF bands that are allocated to the amateur service play a major role in working 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 radio communication 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.”

Currently 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.”

Several countries have already made spectrum in the 5 MHz band available to radio amateurs to carry out propagation studies in preparation for Agenda Item 1.4 discussions in 2015.

The South African Radio League has asked the Independent Communications Authority of South Africa (ICASA) to make frequencies available to South African radio amateurs for a 5 MHz pilot study. While ICASA is not opposed to the proposal, radio amateurs are hoping that it will fast-track the application so that the propagation studies may begin soon. Participants in the study will have to modify existing transceivers which legally cannot be done until ICASA gives the official green light. New antennas will also have to be constructed and erected.

While the propagation of signals is 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.

In a study SOEKOR observed that on the Cape south coast seawards of Mosselbay, in the late afternoon and early evenings, 5 MHz provides E-layer propagation for about an hour or two. This also occurred “up and down” the Outeniqua coastline.

Propagation modelling showed that the E-layer at those times was between 110 and 80 km above 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 either using low power or inefficient antennas, or both.

It would be interesting to see how far and wide this propagation mode does actually occur in South Africa. Radio amateurs can play a major role as they are not constrained by operational requirements or business financial constraints.

The 5 MHz region has much lower levels of static (QRN) than 3 MHz and in preliminary studies it was found that 5 MHz is much better for packet-radio operation (AX25) than 3 MHz.

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