A series of . Nordic conferences on HF communications was initiated in 1986 when HF 86 was held in Sweden. International interest in contributing with papers, exhibits and participants has grown, and the conference that initially was planned for a limited audience of Nordic countries has now an international acclaim.
The 13th issue of HF 19 was held in 12-14 August, at Fårö, Sweden . The participants came from more than 10 countries. The presented papers covered a wide area of aspects of High-Frequency (HF) communications:
- Propagation and Modelling
- Propagation and Spectrum Management
- Signal Processing and Radio Protocols
- Systems and Techniques
- Antenna Systems and Cognitive Radio Systems
- User Scenarios
- User Scenarios and EMC
HF usually means the frequency region of 3 – 30 MHz. Since the wavelength for these frequencies are considerably larger than the dimensions of the platform, one basic challenge is to design electromagnetic efficient antennas. One advantage of this frequency region is that large communication distances can be achieved since the radio wave can be reflected in the ionosphere.
HF communications can therefore cover long distances, without dependency of other infrastructure. This makes it especially valuable in e.g. military and crisis situations. The HF area is still undergoing a strong development e.g. to increase the data rates in the communication links and to further improve signal processing and antenna solutions. The area is therefore of high importance for several applications.
A comparison of HF radio systems and smartphones was done in the paper:
Arnie Johansen, “HF in the smart-phone age: Operational considerations of HF systems”.
The author summarized some properties of HF communications and smartphones. HF communication has historically been seen as undesirable from a number of points of view:
- Slow data rates,
- Inconvenient and difficult to operate,
- Slow and unreliable circuit establishment,
- Manual actions and fine tuning required, and
- Requires specialised knowledge.
This is in contrast to modern capabilities offered by smartphones, tablets and personal computers, which are:
- Convenient and easy to use,
- Provides integrated support for different traffic types, and
- Requiring little communication knowledge from the user.
However, the major benefit of HF is its reach and ability to work in situations when and where nothing else can. It is very resilient against most problems affecting outages of other networks. HF may be the only available long-distance communications medium in a satellite-denied environment. The author discussed the question: “Can we, and should we, seek to make HF communication more similar to smartphones?”. The conclusion was that it can be seen that a large number of the features in smart-phone systems can be applied to HF system design and that this would make HF more usable and attractive to users.
Some of the papers were especially interesting from the perspective of Electromagnetic Compatibility (EMC). These papers presented different kinds of issues related to electromagnetic interference for HF communications. One paper analysed the possibilities of using HF communications for small unmanned aerial vehicles (UAV:s) :
Filip Enander, “On the realisability of HF communications from a very small flying platform”.
The purpose was to investigate the practical possibilities of using HF communications to transmit sensor- and positioning data from a small UAV. The conclusion was that spectrum and interference management becomes critical. Furthermore, for optimal choices of operating frequency, even a small antenna permits low-power operation.
One paper covered experiences of electromagnetic interference from vehicles and the electrified environment in the vicinity of buildings:
Torbjörn Carlsson, “Deployment of HF Radio for the European Union capacity building mission In The Republic of Niger”.
Several interference problems were found during the work of purchasing and integrating an HF communication system on vehicles and for a base and office. Examples of interference sources from vehicles were the engine system and the fan for the AC (air conditioning) system. For the base and office, several man-made interference sources were identified:
- UPS (Uninterruptible Power Source) units
- Some computer power supplies
- Low energy lamps
- Power supplies to computers and mobile phones
- Air conditioning units
The overall conclusion was that electromagnetic interference is a large threat to HF communication in these kinds of missions. It was in general not possible to have an efficient and well-functioning system with the base station near buildings. At a minimum, the antennas must be located as far as possible from any building. Furthermore, it is necessary to minimize interference both at the base station and in vehicles. The vehicles produced significant interference signals in the HF band. The competence for solving these kinds of vehicle problems is also rare according to the authors experience.
Another conclusion was that frequency planning is always essential. Frequencies given by authorities are not always usable for many reasons. The organisation therefore needs to control and test these frequencies, and if necessary propose changes to the local telecommunication authorities.
Two other papers addressed EMC problems caused by man-made interference sources:
Lars Weberg, “Wireless power transfer and the interference situation in the LF-HF bands”.
Peter Stenumgaard, Sara Linder and Henrik Olsson, “Interference impact from solar-panel systems on HF communications”.
Paper 1 covered radiated electromagnetic interference from wireless power transfer for electric vehicles. Technologies to transmit electric power wirelessly have been developed since the 19th century, beginning from induction technology. There are various wireless power transmission (WPT) applications in use, in experimental, or in implementation phase throughout the world. WPT applications are expanding to mobile and portable devices, home appliances and office equipment. The automotive industry looks at WPT for electric vehicle (EV) applications in the upcoming future. The frequencies intended for WPT for electric vehicle charging (WPT-EV) are also used by radiocommunication systems or services. It is therefore of interest to investigate potential interference problems. The frequency region of interest of paper 1 was 10 kHz – 30 MHz, covering both Low Frequency (LF) and High Frequency (HF) communications. Emission limits from several standardization publications were used as a basis for the analyses:
- IEC 61980-1:2015
- IEC TS 61980-2/-3
- ETSI TR 103 409
- ITU-R SM-329
- ETSI EN 300 330
The analysis method compared the received interference level in a communication receiver, with the level of other noise in the receiver (man-made noise for HF, atmospheric noise for LF). For different distances, the interference level exceedance to the noise level was determined. The results showed that significant interference contributions could be expected both in the HF- and LF-band. Therefore, this kind of interference has to be further analysed in the future to ensure that radio-based services will not be disturbed by these power-transfer technologies.
Paper 2 covered electromagnetic interference from solar-panel systems. In recent years, solar energy systems have become more and more widely used. The interference issues connected to these systems have also started to gain interest, since both conducted and radiated electromagnetic emission can be generated by these systems. In this paper, the interference impact on HF communications was analysed for radiated emission measured from a solar-panel system. The results showed that significant impact on the communication performance can arise for solar-panel systems co-located in the vicinity of HF systems. Furthermore, that the communication range of the analysed HF link might be significantly reduced for a co-location distance of 50 meters to the solar-panel system of interest. The overall conclusion is that co-location of solar-panel systems in the vicinity of HF communications must be carefully analysed both before the installation and then regularly, not to create undesired reductions in communication quality.
The interference aspects of wireless power transmission and solar panels will probably be further highlighted in the future, since both areas undergoes rapid developments and that an increased use of both technologies could be expected.
Peter Stenumgaard, Swedish Defence Research Agency (FOI)