Tim Hardy, Nautel's Head of Engineering

Station Power Usage Example

The current average residential rate in the US is close to 12 cents per kilowatt hour and some regions exceed 25 cents. An older tube type 50 kW transmitter might operate with an electrical efficiency factor (RF power output divided by AC power input) of around 70%. Assuming an additional 10 kW of radiated sideband power, this transmitter will consume nearly 86 kW. The daytime yearly energy usage of this station (assuming a 12 hour day) would be 377,000 kilowatt hours per year for an average cost of $45,000. Depending on the night time status, this station could use up to $90,000 annually.

Nautel’s NX Series with an overall efficiency of up to 90% offers a power reduction of 22% and annual savings of up to $20,000.

Other NX Series technologies like Dynamic Carrier Control or Amplitude Modulation Companding can realize additional power reductions of 30% (or more) for total annual savings of $41,000.

Cost savings of this magnitude can repay the capital investment for a new transmitter in just a few years. Over the life of a 50kW transmitter cost savings easily amount to $500,000 – $1,000,000.

Nautel’s NX Series offers:

  • Industry’s top efficiency: up to 90%
  • AM precorrection for increased linearity
  • 2.7 MHz Direct Digital Modulation
  • 17″ intuitive touch screen interface
  • 100% remote access to the user interface
  • RF and audio spectrum analyzer
  • Integral Digital: HD Radio, all DRM modes
  • The new standard in compact AM design

NX Series

Learn more about Nautel’s NX Series AM transmitters with power levels ranging from 1kW to 2000kW


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Saving Power in AM Transmitters


As power levels increase on AM transmitters, electricity may represent a significant cost to the operator. Transmitter technology has improved though, and manufacturers have worked to improve the electrical efficiency through the use of new modulation techniques (such as Pulse Duration Modulation), and new amplifier technology (such as Class-D amplifiers). In addition, advances in semiconductors generally intended for use in Switch Mode Power Supplies have allowed for further gains.

Nautel’s latest AM series, the NX Series, has an overall efficiency of up to 90%. By replacing an older 70% efficient tube transmitter with a modern unit with 90% efficiency the power consumption in the power usage example (see side-bar) would drop by 22%. This translates into annual savings of up to $20,000.

Since the early 1980s, another technology has existed to help reduce the energy costs of AM transmitters. One version of this technology is Dynamic Carrier Control. This system takes advantage of the fact that the majority of the energy in an AM transmission is in the carrier, which contains no information. By dynamically reducing the carrier power depending on the state of the modulation, additional power savings of 30% to 50% may be realized. These systems have been deployed in many high power sites around the world and are used today by major international broadcasters.

Brookmans Park Transmitting Station June 2004

Brookmans Park, London


At the historic (1929) Brookmans Park site outside London a Nautel NX100 was installed recently operating with Amplitude Modulation Companding, another method of power reduction. This site is now operated by Arquiva for the BBC (BBC Radio 5, 909 kHz in the London area) and was used for early trials of AMC technology during its development in 1985. Implementing AMC or DCC today simply involves selecting the appropriate option on the NX100 front panel, instructing the built in DSP based exciter to run the modified carrier algorithm. Because these systems do reduce the power in the carrier, there may be slight impairments in the received signal quality however these problems tend to be slight. An additional 30% reduction in energy in the power usage example (see side-bar) would realize total annual savings of $41,000. Cost savings of this magnitude can repay the capital investment for a new transmitter in just a few years. Over the life of a 50kW transmitter cost savings easily amount to $500,000 – $1,000,000.


Nautel has also developed products for installation on older transmitters that do not have internal signal processing capability. The latest product utilizes an NX series DSP exciter card in a 1U chassis. Modified carrier and audio signals are sent to the host transmitter allowing it to benefit from this technology. While carrier control is currently not legal in the United States, work is underway to start an initial trial with the permission of the FCC. Not surprisingly, this trial will be in Alaska where energy costs can be very high and some transmitters run on diesel generators. While permission has still not been granted, it may not be long before modified carrier levels are broadcast in North America for the first time. Perhaps this technology will make its way into the mainstream in the US and Canada as it already has done elsewhere in the world.

For more information on this topic, please read “Energy Conservation in AM Broadcast Transmitters Using Carrier Control Algorithms”, as presented by Tim Hardy at NAB 2009 more>>

Learn more about MDCL AM Power Saving Technology >


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