Despite the continuing growth in audiences for streaming content, the established broadcasters remain popular. Indeed, market predictions are that, while streaming services will gain viewers and revenue, traditional linear television will remain stable; Statista even suggests a slight rise in daily viewing hours.

Is terrestrial transmission the best way to deliver television channels? In purely practical terms, yes it is. It ensures everyone in the audience views at exactly the same time, with the minimum of latency. Transmitter networks are well-established, and the technology is mature and extremely reliable.

But today we have to consider sustainability. Television transmitters are noted for being heavy users of power, and not particularly efficient in operation. How does the environmental impact of broadcast television stack up against streaming?

There have been some wildly varying estimates of the carbon cost of streaming recently and it is not easy to identify reliable data. Two promising sources put the CO₂ equivalent of an hour of streaming Netflix at 36g (The Shift Project) or 55g (Carbon Trust).

A legacy television transmitter with a 10kW emitted power and 20% efficiency consumes 50kWh. Our World in Data has a useful chart of the carbon intensity of electricity by country (https://ourworldindata.org/grapher/carbon-intensity-electricity). In 2021, it showed wide variations, from 9g CO₂ equivalent per kWh in Sweden to 428g in the UAE; 402g in Germany and 380g in the USA; 265g in the UK and just 67g in nuclear-reliant France.

If we take the UK figure as a rough mean, our transmitter site would produce 13.25kg CO₂ equivalent. Compared to, say, 50g for the streaming service, that is a seemingly disastrous ratio of 265:1.

But, of course, streaming video is a one-to-one connection. If the house next door is watching the same streamed programme at the same time, they are responsible for their own 50g CO₂ equivalent. And a television transmitter is capable of reaching very many more than 265 households – potentially millions - with precisely the same energy consumption.

The first takeaway, then, is that terrestrial television is a very efficient way of delivering content to substantial audiences.

But the legacy transmitter site quoted earlier has an efficiency – the ratio of AC in to radiated power out – of 20%. That really is not very impressive, and it is time to make serious changes to improve the conversion factor.

The next generation of transmitters must focus on optimisation of energy efficiency. There is obviously a direct and significant operational saving if you can reduce the power consumption for the same output quality and coverage, as well as the contribution to sustainability that makes.

New power amplification architectures are now delivering significant improvements in efficiency. These architectures also contribute significantly to resilience, meaning that a transmitter can continue to provide an acceptable output even in the case of partial failure. That means you may not need hot or warm standby electronics, which consume power even though they are not on air.

There is another sustainability issue here, too. New electronic architectures, combined with excellence in physical design to maximise cooling flows and eliminate thermal stress, are more reliable and resilient, which means less emergency maintenance. Add an intelligent control layer which is capable of self-repair and clearly reporting potential problem areas, and there is less need for every transmitter site to be permanently manned, and fewer road journeys with urgent spares are required.

The efficiency of the transmitter site is measured in terms of the ratio of the incoming AC power to the radiated output. That includes all the services of the building as well as the transmitter electronics themselves. Air conditioning is a significant power consumer, and air-cooled transmitters will always need powerful HVAC to take the heat away from the electronics.

Liquid cooling can take the heat not just out of the racks but out of the building where it can be dissipated into the outside environment. This saves an enormous amount of energy for air conditioning, and with that it significantly reduces the carbon footprint of the complete transmitter site.

All of these considerations have led to the TH1 transmitter family from Rohde & Schwarz. The environmental performance will be dependent upon the format and frequency of transmission, but on average it provides 44% energy efficiency (and in some cases as much as 47%).

Going back to our notional 10kW transmitter, it now only needs around 23kW of AC input, so energy costs and carbon outputs are 50% or better than the installed base of transmitters. If we say that the transmitter reaches a million households, then the carbon footprint of each one is a mere 0.006g CO₂ - a very significant boost to environmental performance.