“The strongest RF argument is not the loudest claim. It is the cleanest measurement, taken at the right distance, over the right bandwidth, with the duty cycle included.” – MJ Martin
Introduction
Ed Freen’s LinkedIn comment is a useful reminder of how a technical person should approach radio frequency questions. He did not start with fear, opinion, or social media mythology. He decided to measure. That is the correct instinct. In RF engineering, a transmitter is not judged by rumour. It is judged by frequency, conducted power, antenna gain, equivalent radiated power, duty cycle, separation distance, modulation, exposure averaging period, and compliance limit.
Smart meters are often described online as though they are mysterious, high power, continuous radiation sources. That description is technically wrong. A smart meter endpoint such as an Itron 100W+ ERT module is a low duty cycle telemetry transmitter. It sends short, structured data messages, then remains silent for long intervals relative to the transmission duration. The engineering question is not whether the device emits RF energy. It does. The proper question is how much RF energy is emitted, how often it is emitted, at what frequency, from what antenna system, at what distance, and how that exposure compares to recognized safety limits.
In this paper, we will consider the most popular smart meter technology, the Itron ERT. These radios can be found in water, gas, and electric meters in Canada. In addition to the focus on the Itron ERT radio, we will also consider the Canadian perspectives.
The Itron 100W+ ERT as an RF Device
The Itron 100W+ ERT module is a radio endpoint used in utility metering. It is associated with water metering applications, but the broader ERT family is used across water, gas, and electric meter reading systems. The transmitter operates in the 915 MHz region, which is within the 902 to 928 MHz industrial, scientific, and medical band commonly used for licence exempt telemetry and spread spectrum utility communications.
The supplied 100W+ RF specification identifies two primary operating behaviours: Secure Mobile Mode and Secure Network Mode. These modes are important because the exposure case is not a single number. It depends on message type, interval, transmission duration, transmitter power, and antenna gain.
In Secure Mobile Mode, the 100W+ uses SCM+ secure transmission. The transmission duration is 13.18 milliseconds and the transmission interval is once every 10 seconds. The transmitter power is 8.54 dBm, equivalent to approximately 7.14 milliwatts at 915 MHz. The antenna gain used for the maximum permissible exposure calculation is 6.73 dBi, or 4.710 numeric. At a 20 centimetre separation distance, the stated power density is 0.00669 milliwatts per square centimetre.
The key parameter is duty cycle. A 13.18 millisecond transmission every 10 seconds produces a duty cycle of 0.001318. That means the transmitter is active for only 0.1318 percent of the time in that mode. The remaining 99.8682 percent of the time, that specific transmission mode is not radiating.
Secure Mobile Mode Exposure Calculation
The majority of Canadian small- to mid-sized Utility operators make use of the Itron ERTs configured in the Mobile Mode for Walk-by, Drive-by, or Fly-by collection of the meter’s monthly consumption of the resource – water, gas, or electricity. The applicable maximum permissible exposure (MPE) limit in the supplied specification is 0.61 milliwatts per square centimetre, based on a 30 minute FCC averaging basis (Note: ISED, the Canadian Government Department responsible for frequency assignments makes use of the same specifications for this ISM Band spectral assignment as is used by the FCC in the United states). At 20 centimetres, the peak power density for Secure Mobile Mode is 0.00669 milliwatts per square centimetre. Dividing 0.00669 by 0.61 gives 0.011, or approximately 1.1 percent of the MPE limit.
Even that number is a peak comparison at 20 centimetres. It does not yet account for the fact that the transmitter is active only briefly. Once the duty cycle is applied, the average exposure becomes 0.001318 multiplied by 0.011, which equals approximately 1.45 times 10 to the minus 5 of the MPE limit. Expressed as a percentage, the duty cycle corrected exposure is approximately 0.00145 percent of the MPE limit.
This is the part that many non technical internet discussions miss. A peak detector may respond to a burst, but regulatory exposure is generally evaluated using averaging concepts. A device that transmits for 13.18 milliseconds every 10 seconds is not equivalent to a transmitter radiating continuously at the same instantaneous field level.
Secure Network Mode Exposure Calculation
Many larger Canadian Utility Operators make use of AMI networks so they use the Secure Network Mode contains three transmission types. The first is SCM+ secure AM, with a 13.18 millisecond duration once every 60 seconds. It uses 8.54 dBm, or 7.14 milliwatts, at 915 MHz, with the same 0.00669 milliwatts per square centimetre power density at 20 centimetres. The duty cycle is 13.18 milliseconds divided by 60 seconds, or 2.197 times 10 to the minus 4.
The second transmission type is the Network Interval Message, secure FM. It has a duration of 12.16 milliseconds and an interval of once every 360 seconds. The transmitter power is higher, at 25.89 dBm, or approximately 388.15 milliwatts at 915 MHz. The antenna gain used in the exposure filing is 6.11 dBi, or 4.083 numeric. The stated power density at 20 centimetres is 0.315 milliwatts per square centimetre. The duty cycle is 3.378 times 10 to the minus 5.
The third transmission type is the secure leak sensor message. It has a 7.68 millisecond duration and an interval of once every 3540 seconds. It uses the same 25.89 dBm transmitter power and 6.11 dBi antenna gain basis as the Network Interval Message. The stated power density at 20 centimetres is again 0.315 milliwatts per square centimetre. Its duty cycle is 2.169 times 10 to the minus 6.
The highest peak exposure case in Secure Network Mode is 0.315 divided by 0.61, which equals approximately 0.516, or 52 percent of the MPE limit at 20 centimetres. That sounds substantial until time is included. The transmissions are extremely short and infrequent. Applying the duty cycle corrected calculation across the three message types gives approximately 2.1 times 10 to the minus 5 of the MPE limit, or 0.0021 percent of the MPE limit. That is the proper engineering conclusion for average exposure.
Why Duty Cycle Matters
Duty cycle is not a technical trick. It is central to RF exposure evaluation. A continuous transmitter and a burst transmitter with the same instantaneous power density do not produce the same time averaged exposure. The 100W+ ERT is not a broadcast station, a cellular base station, or a microwave oven. It is a telemetry endpoint that wakes up, transmits a short encoded message, and returns to a low activity state.
The difference between peak and average exposure is especially important when discussing smart meters with the public. A broadband RF meter may show a pulse. A spectrum analyzer may show energy at 915 MHz. A near field probe may show a response close to the enclosure. None of that is surprising. The question is whether the measurement is calibrated, whether the antenna is appropriate, whether the instrument bandwidth is suitable, whether the distance is defined, whether the duty cycle is included, and whether the result is compared to the correct regulatory limit.
Ionizing and Non Ionizing Radiation
The word radiation is frequently misused. Ionizing radiation includes X rays and gamma rays. These forms of electromagnetic energy have photon energies high enough to remove electrons from atoms and break chemical bonds. That is why ionizing radiation is treated differently in health physics.
Radio frequency energy at 915 MHz is non ionizing. It does not have sufficient photon energy to ionize atoms or directly break DNA bonds. At RF frequencies, the established biological effect at sufficiently high exposure levels is heating. That is why RF exposure standards focus on power density, specific absorption rate, field strength, time averaging, and safety margins.
This distinction does not mean RF exposure is ignored. It means it must be evaluated using the correct physics. Treating a 915 MHz meter transmitter as though it were an X ray source is not conservative engineering. It is category error.
Safety Code 6 and Canadian Context
In Canada, Health Canada’s Safety Code 6 is the central reference for limiting human exposure to radiofrequency electromagnetic energy. It applies across the frequency range from 3 kHz to 300 GHz and is used to establish exposure limits for RF fields. This range includes smart meters, WiFi equipment, cellular devices, Bluetooth devices, and other common radio systems.
Safety Code 6 is based on recognized biological effects and incorporates safety margins. Above 100 kHz, the principal established effect addressed by the limits is tissue heating. This is directly relevant to smart meters because 915 MHz is well above 100 kHz. The correct Canadian discussion is therefore not whether the meter emits non ionizing RF energy, but whether the field levels are below the applicable exposure limits when assessed using proper measurement and averaging methods.
Comparison with Common Household RF Sources
A smart meter endpoint is usually mounted on the exterior of a building or inside a meter pit. The user is typically separated from the endpoint by distance, wall materials, meter enclosures, or soil and pit structures. By comparison, a smartphone may be held directly against the head or carried against the body. A WiFi router may transmit frequently inside the living space. Bluetooth earbuds operate extremely close to tissue. A laptop or tablet may maintain continuous wireless connectivity only centimetres from the user.
Microwave ovens operate at much higher internal RF power, commonly around 2.45 GHz, although they are shielded and regulated for leakage. The comparison is not that a microwave oven and a smart meter are equivalent. They are not. The comparison is that household RF exposure must be understood by power, shielding, distance, duty cycle, and use pattern. In that engineering framework, a low duty cycle 915 MHz ERT mounted away from normal body contact is usually a small contributor to total household RF exposure.
The Problem with Mythological Data
The internet contains a large volume of smart meter content that looks technical but is not technically meaningful. Common errors include using uncalibrated handheld meters, measuring in unknown bandwidths, presenting peak readings without time averaging, confusing near field and far field conditions, ignoring duty cycle, mixing magnetic field and RF power density terminology, or comparing non ionizing RF energy to ionizing radiation.
A credible RF assessment must state the frequency, measurement distance, antenna correction factors, detector mode, bandwidth, calibration status, averaging time, transmitter duty cycle, and applicable exposure limit. Without those details, the result may be visually dramatic but scientifically weak. In engineering terms, unexplained numbers are not evidence. They are only numbers.
Summary
The Itron 100W+ ERT is a low duty cycle utility telemetry transmitter operating around 915 MHz. In the supplied Secure Mobile Mode case, the peak 20 centimetre exposure is approximately 1.1 percent of the MPE limit, and the duty cycle corrected exposure is approximately 0.00145 percent of that limit. In the supplied Secure Network Mode case, the highest peak exposure is approximately 52 percent of the MPE limit at 20 centimetres, but the combined duty cycle corrected exposure is approximately 0.0021 percent of the limit.
Those results are not slogans. They are engineering calculations based on power, antenna gain, distance, message duration, message interval, and exposure limit. The proper conclusion is that smart meter RF should be measured and discussed honestly, but not mythologized. When evaluated under the correct RF framework, the smart meter is not a mysterious radiation hazard. It is a short burst, low duty cycle, non ionizing telemetry radio that meets the applicable RF compliance framework when used as specified.
Citation
Health Canada states that Safety Code 6 sets recommended limits for human exposure to radiofrequency electromagnetic fields from 3 kHz to 300 GHz. (Canada) Health Canada’s published Safety Code 6 document states that its purpose is to establish safety limits for human exposure to RF fields in that same frequency range. (Canada) Health Canada also states that smart meter RF exposure levels are far below Canadian safety limits and that no precautionary measures are needed to reduce RF exposure from smart meters. (Canada)
About the Author:
Michael Martin is the Vice President of Technology with Metercor Inc., a Smart Meter, IoT, and Smart City systems integrator based in Canada. He has more than 40 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He was a senior executive consultant for 15 years with IBM, where he worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin served on the Board of Directors for TeraGo Inc (TGO: TSX) and on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now Ontario Tech University] and on the Board of Advisers of five different Colleges in Ontario – Centennial College, Humber College, George Brown College, Durham College, Ryerson Polytechnic University [now Toronto Metropolitan University]. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees – in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and seven major certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has completed over 80 next generation MOOC (Massive Open Online Courses) [aka Micro Learning] continuous education programs in a wide variety of topics, including: Economics, Python Programming, Internet of Things, Cloud, Artificial Intelligence and Cognitive systems, Blockchain, Agile, Power BI, Big Data, Design Thinking, Security, Indigenous Canada awareness, and more.
Martin in a volunteer, a photographer, a learner, a technologist, a philosophizer, and a romantic optimist.