How does hf communications work

Why you need a high-power HF transmitter. Previous News. Next News. Subscribe Register For Barrett news and updates Register. This website uses cookies to improve your experience. We'll assume you're happy with this. Accept Read More. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are as essential for the working of basic functionalities of the website.

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Necessary Necessary. The chosen frequency may sometimes only be good for a limited period during the flight as the contact frequency varies depending on the time of day and geographic location. We recommend that you periodically call STO Radio during the flight to check if it is necessary to choose a new frequency.

Airlines that adopt this standard operating procedure rarely experience difficulties in contacting their flights through STO Radio. This is especially important for long haul flights.

That means you need to:. The reason is simply to optimise the use of our equipment. We try to avoid blocking the monitored frequencies with phone patches in case other flights want to call in. Please remember to return to one of our monitored frequencies to resume SELCAL guard after completion of communications on the alternate frequency unless otherwise instructed. Refresh your memory How does HF Radio work? Guide How does HF Radio work? First, try to call again a couple of times on the same frequency.

Then, try another frequency. The ionisation in the ionosphere is chiefly caused by radiation from the Sun. As a result the state of the Sun and the radiation received from it governs the state of the ionosphere and HF propagation. The Sun: The Sun is a fascinating star - discovering all about it is fascinating it is own right. Despite this, our Sun is the main source of radiation that creates the ionosphere. Their presence leads to higher levels of radiation being emitted and therefore this affects HF propagation.

Sunspots have been recognised in the surface of the Sun for very many years, and their affect of radio propagation was noted once the way in which signals travelled over long distances started to be understood. It was found that there was a correlation between sunspots and the conditions for HF radio propagation and radio communications.

Solar disturbances: From time to time, massive disturbances occur on the surface of the Sun. Solar flares, and coronal mass ejections, CMEs also give rise to increased levels of radiation which in turn affects HF propagation. Smaller increases in radiation level can improve the HF radio conditions, but as they increase, it can even lead to a radio blackout on HF. Visible signs of solar disturbances can be visible auroras at the poles. For large solar disturbances, ionisation levels at the poles increase significantly and can allow some specialist propagation modes at VHF allowing radio communications to be established at these frequencies.

Here stations point their antennas northwards and reflections can often be heard over reasonably long distances. HF propagation using the ionosphere is still a widely used as a form of radio communications.

While not as reliable as satellite communications, it is not nearly as expensive, and can provide a useful back-up in case the satellite communications fail. HF propagation is also widely used for broadcasting, military and many other organisations requiring long distance communications.

HF propagation is also widely used by radio amateurs who are able to communicate across the globe. Under some circumstances it is possible to use low power levels and simple antennas to establish radio communications over long distances.

As a result HF propagation using the ionosphere is likely to remain in use indefinitely as a form of radio communications technology.

HF ionospheric propagation applications Using HF propagation via the ionosphere, radio signals can be heard around the globe — it was this form of communication that first opened up many global links to inaccessible regions, and also enabled international broadcasting.

Typical antenna used for HF radio communications via the ionosphere Radio amateurs or radio hams also make widespread use of HF propagation via the ionosphere, often establishing radio communications with distant points on the globe with low powers and modest antenna systems. The main regions are detailed below: D region: When a sky wave leaves the Earth's surface and travels upwards, the first region of interest that it reaches in the ionosphere is called the D region.

This region attenuates the signals as they pass through. The level of attenuation depends on the frequency. Low frequencies are attenuated more than higher ones. E region: Once the signals have passed through the D region, they reach the E region.