An ionosonde is a special HF radio transmitter that periodically transmits a signal that sweeps across a large portion or the entire HF spectrum to identify the propagation of radio signal in the ionosphere, currently they are operated by various institutions around the world.

To my knowledge, in order to legally operate a radio transmitter at a frequency/band, the frequency must be allocated by regulatory agencies for use by the type of service that the transmitter belongs to. Ultimately, all radio transmissions must be legal under the ITU Radio Regulations.

How does the ITU Radio Regulations apply to an ionosonde? Why is it legal for an ionosonde to use a huge portion of the spectrum, which otherwise wouldn't be possible for conventional radio communication services?

  • $\begingroup$ Probably the ionosonde would need to get an experimental license. You might want to look for scholarly papers on them and see if any mention this. $\endgroup$
    – user10489
    Commented Mar 1, 2020 at 22:12

1 Answer 1


Some googling for "ionosonde operation" reveals some applications (for example) to the FCC to operate under 47 C.F.R. §§ 5.3(c) and (e) which details that "Stations operating in the Experimental Radio Service will be permitted to conduct the following type of operations".

So it seems that ionosondes in the US are governed by the FCC rules of the Experimental Radio Service. There may be other services that also govern long term use such as those operated by NOAA/NCEI.

These licensures by the FCC seem to satisfy the ITU requirements.

  • 1
    $\begingroup$ The OP's profile indicates that he lives in China. But since he didn't mention that, upvoted. :-) $\endgroup$ Commented Aug 20, 2020 at 19:50

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