Radio amateurs step up HF noise floor monitoring

September 13th, 2017, Published in Articles: EngineerIT

It is a well-known fact that many new electronics devices becoming available on South African market do not comply with EMC and EMI standards. In many instances standards and regulations cannot keep up with technology developments often resulting in unintended interference consequences affecting radio communication.

Some of the current developments include magnetic charging devices of which electric car chargers are a major future source of RF interference. Just image if every household had two chargers in their garage. Currently there are no agreed EMC standards for electric car chargers. The industry’s main interest is efficiency with little attention paid to possible RF interference. A number of bodies such as ETSI, CEPT, CISPR and ITU are looking at the issues with industry lobbying for the widest possible limits. These new technologies could generate unintended RF signals that could interference with other communication systems such as ADSL and VDSL.

There are other sources of RF interference such common items as load controllers for geysers, solar panels and their associated control systems, to mention some. Earlier this year the South African Radio League held a workshop to discuss how best radio amateurs can become involved in monitoring the perceived increase in the level of the radio frequency noise floor. At a second workshop held in August, plans for an automated monitoring system were agreed.

Fig. 1: Block diagram of the SARL HF noise level monitoring system.

While just about every organisation involved in radio communication agrees that it is becoming a major problem, the lack of actual measurement of the noise floor is lacking. Is the problem as great as we make it out to be? All the evidence produced thus far is anecdotal. For example when radio pioneer John Streeter made the first radio contact between South Africa and the USA on 18 September 1925 at five minutes past mid-night on 36 metres, he used a low power transmitter, simple antenna and crude receiving equipment. It would today be totally impossible to emulate his feat due to the very high RF noise levels compared to the levels in 1925. There simply was no RF noise.

The SARL is a member of the TC73 committee (EMC) of the South African Bureau of standards and has proposed to the committee that the monitoring and study of the high level increases in the HF noise floor is an emerging need. The proposal was accepted  which means it will be on the agenda of the next meeting as well as an agenda item for Workgroup 6 of TC73. The SARL is in the process of setting up a steering group to encourage radio amateurs to take an interest and join the SARL monitoring group. The main purpose of the steering group is to promote and facilitate the project.

At the August workshop, facilitated by AMSATSA and the SARL, it was agreed to take the HF dongle route and use a raspberry pi to provide the compute power required. Anton Janovsky (ZR6AIC) has developed a system as shown in Fig. 1 which is currently being tested.

The HF noise monitoring system takes 1 MHz bandwidth samples every two minutes using the rtl-power utility and saves the measurements in a CVS file. The two minute scheduling is done with 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 CVS files are created and appended as the measurements are made. A Perl script utility is then executed from a cron scheduler to read the 29 CSV files and import the data into a RRD database.

 

Fig. 2: Snapshot of 7 MHz graph. The high spikes are local AM transmitters.

To view the system in operation, you can link to the live system here. The system also records the waterfall image. Live images can be viewed here.

Fig. 3: Snapshot of the waterfall.

Limitations

To enable to make comparisons between all stations participating in the project, a standard calibrated antenna would have to be used.  Monitoring over a wide spectrum complicates the calibrated antenna issue. A small SARL team is studying this and welcomes input from interested persons. Input can be sent by email to sarlregwg@sarl.org.za.

To get as many amateurs involved in the project it was decided, at this stage, not to focus on a calibrated antenna. This is a long term project in which various antennas are under consideration and will be tested.

The interim objective is to monitor the RF noise level in each station’s local area and compare results over a period of time. As soon as server facilities become available, data from each participating station will be stored in its own file for further analysis and comparison over a period of time.

Commenting on the project, SARL president Nico van Rensburg (ZS6QL) said that in addition to the current initiatives and as more individuals become involved, a national study group will be established to discuss on a regular basis methods to deal with man-made noise affecting amateur radio frequencies. “I believe it is a step in the right direction.”

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