Amateur radio societies concerned about the HF noise floor

April 23rd, 2019, Published in Articles: EngineerIT

The International Amateur Radio Union and many of its member societies are expressing serious concerns about the increasing high frequency (HF) spectrum noise floor and are making their voices heard. It was in June 2016 that the world started taking note, when the Federal Communications Commission (FCC) office of engineering and technology technical advisory council (TAC) opened a noise floor technical inquiry in the form of ET docket no. 16-191. The aim of the FCC investigation was to seek answers to a few 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 TAC technical inquiry was an unmistakable consensus among the respondents: A noise floor study is not only needed but overdue.

An IEEE EMC paper authored by Koos Fockens, Peter Zwamborn and Frank Leferink, showed that tests carried out in 54 different locations in the Netherlands over past decade uncovered that there was a statically significant increase in the man-made radio noise (MMN floor) in comparison with ITU-R reference levels. The paper, entitled “Measurement methodology and results of measurements of the man-made noise floor on HF in the Netherlands”, refers to measurements made in various locations from lakes and woods at far distances, from built-up areas to residential areas in various densities of habitation and in city centres. As expected, the increase of the MMN floor was the highest in built-up regions.

The authors concluded that the data about man-made noise in ITU-R P.372 – 13 needs updating and made the suggestion for new values for the relevant parameters. Their measurement and analysis have confirmed the accumulation effect caused by the increasing density of interfering sources in close proximity. From their observations it can be concluded that the paradigm of man-made noise has shifted over time. In conventual EMC standards it is assumed that only one single sub-system is present in the close proximity of the receiver, but clearly that is not the case anymore.

The problem of the increasing HF noise floor is partly due to the poorly designed devices on the market such, as LED lights, induction cooking appliances and a host of other electronics but there is larger problem looming, the charging of electric cars. In a report issued in January this year by the European Conference of Postal and Telecommunications Administrations (CEPT) Electronic Committee, the impact of wireless power transmission for electric vehicles (WPT-EV) in 79-90 kHz on radiocommunication services operating below 30 MHz a looming problem. The effect on services operating in adjacent frequencies as well as the impact of unwanted emissions from WPT-EV was studied. Inputs have been made for some radiocommunication services (i.e. standard frequency and time signal service, broadcasting service, amateur service, radio navigation service and fixed and mobile service) and a radio application (EAS) about the potential impact.

The WPT-EV manufacturers have confirmed that systems have been designed to meet the emission limits for inductive short range devices (SRDs) in ERC Recommendation 74-01. The report shows that these limits fall well short of providing adequate protection for the services studied.

For the amateur service, given the planned density of WPT-EV systems, it is calculated that there will be a widespread and serious impact on its operation in the vicinity of WPT systems should spurious emissions, measured at 10 m, be at the current limits of ERC Recommendation 74-01. An appropriate limit at 10 m would be: -46 dBµA/m at 300 kHz reducing by 7 dB per frequency decade to -60.0 dBµA/m at 30 MHz. This can be relaxed by 20 dB if all WPT systems adopt a single common frequency of operation.

WPT-EV is an emerging and evolving technology. To ensure a low probability of harmful interference to radiocommunication services, further study is required, including evaluation of real equipment, mitigation techniques and other measures to improve WPT-EV systems. The ERC recommendation of 74-01 (12) for WPT-EV is inappropriate. The specification is for short range devices like cellphones and small device chargers like toothbrushes, and not for a WPT-EV device that requires up to 22 kW of power.

Radio amateurs are very aware of the problem and have started projects to measure the noise floor. The German Amateur Radio Society (DARC) is working on a system that is close to the ITU-R measurement methods. They are using an active vertical antenna (active E-field probes). The receivers are based on a Red Pitaya using 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 during 2019.

The South African Radio League (SARL) is taking a different approach. It is encouraging radio amateurs to set up their own HF noise monitoring systems using a dongle and a Raspberry Pi. A number of stations are already in place and streaming data to a national server.

Fig. 1: Prototype HF noise floor monitoring system using a RTL dongle and a Raspberry Pi. It will soon be installed at the Jeugland Radio Club in Kempton Park and at the National Amateur Radio Centre in Radiokop, Roodepoort.

 

Snapshot of noise level on the 7 MHz band measured on 23 April 2019

The SARL HF noise monitoring system takes a 12 x 1 MHz bandwidth sample every two minutes using the RTL power utility and saves the measurements in a CVS file. The two-minute scheduling is done with a Crontab calling a script in the HF-noise directory. The RF samples are taken at a 1 MHz bandwidth from 1 MHz to 30 MHz, therefore 29 of CVS files are created and get appended as the measurements are made.

The data recorded is at this stage not calibrated data as individual stations use different antennas and dongle arrangements. The SARL is working on a project to develop a standard antenna which can be calibrated. Currently, the system is used to show trends over time at individual stations and has already been used by individual radio amateurs to resolve noise issues in their areas. The system is under continuous development.

The SARL project is a start and is making radio amateurs more aware of the looming problems and encouraging them to start mitigating noise problems in their own area.

The SARL submitted a paper to the International Amateur Radio Union Interim meeting in Vienna on 27 April 2019 urging other national amateur radio societies to join the initiative.

Fig. 2: Snapshot of noise level on the 7 MHz band measured on 23 April 2019.

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