RF noise is killing communication

September 2nd, 2019, Published in Articles: EngineerIT, Featured: EngineerIT

What climate change is doing to cause erratic and unforeseen weather, so is uncontrolled increases in radio frequency (RF) noise affecting communications, eventually leading to disruption. Like climate change, there are many who doubt its existence and claim it is just a passing phase.

The increasing level of the RF noise floor is created by man-made devices that most people use in their homes: LED lights, electricity savings lamps and RF-heated cooking devices to mention but a few. An even greater disaster looming is wireless power transmission for electric vehicles (WPT-EV). It represents a threat to the radio spectrum not just because of the power involved (up to 22 kW) but the richness of the harmonic content of the emissions reaching well into the VHF radio spectrum, the duration of charging (measured in hours), and the projected density of deployment in residential areas.

It is true that not all these devices will cause interference, as their design and manufacture includes filters and screening to mitigate interference. Currently, international bodies such as CISPR are working on setting limits which these devices and equipment must meet. However, agreeing on limits is a long and drawn out process. As many organisations involved in the communications industry call for stricter and more stringent limits, the electrical and electronic industry is calling for more lenient limits. Another issue which is currently not taken into account is the cumulative effect of noise generating devices. Some discussions have started on this subject but are only at the stage of “Is it a problem and should it be investigated?”

Nobody can afford to sit back, because even if the desired noise limits are agreed, there are many rogue manufacturers and dealers who will happily sell “noise generating” devices, leaving out filter circuits to cut costs.

An IEEE EMC paper authored by Koos Fockens, Peter Zwamborn and Frank Leferink, described tests carried out in 54 different locations in the Netherlands over the past decade, which showed there was a statistical increase in the man-made radio noise (MMN floor) in comparison with International Telecommunication Union Radiocommunication (ITU-R) reference levels. The paper refers to measurements made in various locations from lakes and forests at far distances from built-up areas, to residential areas with varying densities of habitation, as well as city centres. As expected, the increase of the MMN floor was the highest in built-up areas.

The authors conclude that the ITU-R’s data about man-made noise needs updating and made the suggestion for new values for the relevant parameters. Their measurement and analysis have confirmed the cumulative effect caused by the increasing density of interfering sources in close proximity. From their observations, it can be concluded that the paradigm of MMN has shifted over time. In conventional EMC standards it is assumed that only one single sub-system is present, in close proximity to the receiver but clearly that is not the case anymore!

On 15 June 2016, the FCC Office of Engineering and Technology Technical Advisory Council opened a noise floor technical inquiry to seek answers to the following basic questions:

  • Is there a noise problem?
  • Where does the problem exist? Spectrally? Spatially? Temporally?
  • Is there quantitative evidence of the overall increase in the total integrated noise floor across various segments of the radio frequency spectrum?
  • How should a noise study be performed?

Unfortunately, most feedback was anecdotal and not accompanied by measured quantitative data. This is largely because the respondents did not have the instrumentation resources nor the budget to provide the quantitative evidence being sought. Despite the scarcity of quantitative data submissions, one clear outcome of this inquiry was an unmistakable consensus that a noise floor study is not only needed but overdue.

Perhaps the most important question asked was, “Is there quantitative evidence of the overall increase in the total integrated noise floor across various segments of the radio frequency spectrum?” The answer is no. So are we repeating the climate change scenario and waiting till it is too late? Who should be responsible to initiate such a study? Do we have the right tools to do mass monitoring and convince regulatory authorities like Independent Communications Authority of South Africa (ICASA) and the National Regulator for Compulsory Specifications (NRCS) that we have a looming problem and its needs their attention?

Currently, the radio amateur fraternity and other users of weak signal communication are already feeling the pinch. The German Amateur Radio Society (DARC) has developed a system that is close to the ITU-R measurement methods. They are using an active vertical antenna (active E-field probes). The receivers use different input bandwidths. Each receiver has a dynamic range of 100+ dB. By applying two receivers in parallel, the dynamic range is extended significantly. DARC plans to roll out 50 systems around Germany during 2019/2020, which will report to a central server.

An inexpensive noise monitoring system based on a raspberry PI and RTL dongle currently being tested in South Africa

In South Africa, a simpler system is being implemented using a Raspberry PI, an HF dongle, an antenna, and specially written software taking samples at a 1 MHz bandwidth from 1 MHz to 30 MHz and uploading the information to a central server. Experiments are still being carried out to develop an active antenna and calibration software that will compensation for differences in installations. The concept is based on Citizen Science and aims to have systems hosted in different parts of the country, ideally at technical institutions of learning. Here is considerable scope for academic intuitions to make a valuable contribution not just in monitoring, but also developing algorithms to interrogate the massive amount of data collected.

If we do not measure it, identify the cause, we can do nothing about it. When we one day wake up and the phones don’t work and the radio spurt out just noise, it may be just too late!

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