How to set-up a Small Scale DAB Transmission Multiplex

A multiplex owner will:

Need substantial set-up capital
Be required to host several other broadcasters' stations
Have substantial ongoing running costs

The UK regulator recently trialled small-scale DAB multiplexes in various parts of the UK using lower cost open-source processes now available.

Whilst software to achieve encoding, multiplexing and modulation stages of DAB transmissions are now in the public domain, configuring such software to run on proprietary Linux computer platforms is extremely complex and not for the feint hearted. In any case, some critical open-source aspects which can aid system reliability and increase efficiency are yet to be developed.

In short, cost savings can be made for the multiplexing stage but, until software modulators have evolved further, transmitting is best performed by proper broadcast modulators in professional DAB transmitters. SDR solutions without pre-correction result in 'power hungry' inefficient RF implementations. In any case, there is very little actual cost-saving achieved by implementing SDR modulation over a proper DAB transmitter.

Unlike FM, a DAB transmitter broadcasts a 'bundle' of digital carriers across a widespread frequency, containing the digital audio for several stations plus the associated data and error correction information. In very loose terms, a 200W DAB transmitter is like a 2kW FM transmitter, due to the widespread carriers and peak powers involved. Such linear RF power amplifiers are far more complex than those used in FM broadcasting. They also take a lot more power (electricity) but, because several stations are broadcast by one transmitter, running costs and spectrum use are actually much more efficient than the equivalent services on FM. With careful planning and network design, transmitter operators can keep both the initial equipment costs and ongoing power consumption costs down. For example, in existing major networks, transmitter locations are carefully chosen so that antenna gain can be used, whilst still reaching all target areas.

Figure 1. A transmitter location to one side of the coverage area is ideal for DAB.

In short, it seems that the main cost-saving over traditional DAB broadcasting can only, in reality, be achieved at the audio encoding and multiplexing stages. With in-depth Linux computing knowledge and expertise in DAB multiplex technical parameters, a small scale operator can set up their own multiplexing system. They will also need to manage and maintain it, configuring technical parameters for each service, as part of on-going operational changes.

There are many ways in which a multiplex can be realised. Some are shown below, and can use any combination.

Figure 2. Typical SSDAB installation. One station shown, others would also address their CODEC to the multiplexer over fibre broadband

Figure 3. As above, but with contributors linked by STL to central encoding and multiplexing

Figure 4. All broadcasters co-located with the transmitter

If a new multiplex operator feels able to do this, plus set up their own methods of programme delivery networks for each network, the only additional items required would be a transmitter, filter and antenna. For those who prefer to have this part planned, installed, configured and maintained (often remotely, by connected experts) we can offer ongoing service plans.

Before attempting to address equipment costs, we suggest that you create a business model;

Who are the broadcasters interested in joining your Small Scale multiplex?
How many in total?
What are their expectations of business terms and the rental costs?
Where are they located and how will the encoded program feed reach your multiplexer location?
Do you need to install data networks between studios and the multiplexer location?
Is your multiplexer equipment at the transmitter location or do you require a further data connection to the transmitter site?
Is the transmitter site location suitable for efficient coverage of your target area using directional antennas with gain?
What is the technical scope of your awarded licence, including permitted ERP and directional constraints?

Only when armed with this information will it be possible to begin ascertaining the likely capital costs of the RF transmission equipment required. When you have this information, please do contact us so that we can assist with pricing, but please also bear in mind that the UK regulator has yet to decide the technical scope, and each licence with differ.

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