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How does HF Radio work?

Radio communications in the HF band (High Frequency band) are bounced off the ionosphere. The ionosphere is a section of the upper atmosphere which is ionized by solar radiation. This phenomenon influences radio propagation as the conditions constantly change. Since the ionosphere's existence is due to radiation from the sun striking the atmosphere, the effects on Radio communications in the HF-band will vary depending on the time of day (day or night), and also the time of year (winter or summer) as a result of solar radiation from sun spots

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Communicating with STORADIO

  • General
  • Troubleshooting
  • Always USB-mode

The key to successful and reliable HF Radio communications is not only reliant on geomagnetic conditions and equipment. Pilot skills and experience are also very important, when adjusting to the conditions that can quickly change during the flight.

Always consult our HF Propagation chart, before contacting STO Radio. Locate the graphon the Propagation Forecast that best corresponds to your position and choose the nearest STO Radio frequency. Be persistent when trying to establish contact on HF-radio. By persistently trying alternative frequency bands and repeating unsuccessful calls after a few minutes can significantly extend the approximate coverage area available.

What should I do if I don’t receive a response?

  1. First, try to call again a couple of times on the same frequency.
  2. Then, try another frequency.
  3. Then, try again in 15-30 minutes. (It is more likely then that a change in aircraft position or conditions will result in successful contact)

HF radio should always be in USB-mode (Upper Side Band) and not in AM mode. The radio talk must be as clear and concise as possible to avoid any misunderstanding. Use short sentences, and where necessary repeat your message to ensure that it is received and understood. When contacting STO Radio, always provide the following information:

  • Flight number / Registration
  • Approximate geographic location
  • The HF frequency used to call.

This will enable the radio operator to select a suitable transmitter and expedite good communications. Please allow 30 seconds for antenna positioning. Our operators at STORADIO listen for voice calls on six monitored kHz frequencies: 3494/23210, 5541, 8930, 11345, 13342, and 17916. The calls are audible on several directional loudspeakers with at least three loudspeakers for each frequency.

The SELCAL function of the HF-radio is important. We recommend that the pilot makes an initial SELCAL check with STO Radio when departing and remain on SELCAL Guard with STO Radio. It is not necessary to constantly listen to the noisy HF-frequency. The volume can be turned down, but not off. The pilot will then be alerted by an optical or acoustic signal when Stockholmradio has traffic for him/her. 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.

When STO Radio responds to a SELCAL check, our normal procedure is to send a message (via SITA or Email) to your Operations/Dispatch advising them that the flight has Logged On to STO radio and are contactable directly via SELCAL. Airlines that adopt this standard operating procedure rarely experience difficulties in contacting their flights through STO Radio. If SELCAL watch is not maintained on our frequencies, the crew may never be aware of STO Radio’s efforts to call them. Also neglecting to adjust the frequency selection for SELCAL watch during flight will result in degraded or unavailable Ground-to-Air HF contact. This is especially important for long haul flights.

Air-to-Ground calls under normal solar/geomagnetic conditions are usually the easiest to accomplish. The pilot selects a frequency from our HF Radio Propagation Forecast and Calls STO Radio.

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Why do I sometimes receive the transmissions from STO radio that are totally garbled?

The reason for this is most likely that your HF radio is set in “AM" mode. The setting should always be “USB" mode.

Do I have to actually tune my HF radio in order to be able to receive your SELCAL transmissions?

The onboard SELCAL decoder is connected to the receiver of the HF equipment. That means you need to: 

  • Have the HF turned on.
  • Be in USB mode.
  • Have the frequency dials set on a suitable frequency (determined by your location and the time of day). Note: you don’t have to tune the transmitter (by keying the microphone) until you actually need to call us. 

Why is it that you send me to another frequency when I read you perfectly OK on the first frequency?

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. 

What are the charges for using STO Radio services?

 Details of all charges are available at here