  Radio waves provide a useful diagnostic tool to investigate the properties of
the ionosphere because the ionosphere affects the transmission and properties
of High Frequency (HF) electromagnetic waves. We have conducted a
transionospheric HF-propagation research campaign with a nanosatellite on a
low-Earth polar orbit and the EISCAT HF transmitter facility in Troms{\o},
Norway, in December 2020. In the active measurement, the EISCAT HF facility
transmitted sinusoidal 7.953 MHz signal which was received with the HEARER
radio spectrometer onboard 1 Unit (size: 10 cm x 10 cm x 10 cm) Suomi 100 space
weather nanosatellite. Data analysis showed that the EISCAT HF signal was
detected with the satellite's radio spectrometer when the satellite was the
closest to the heater along its orbit. Part of the observed variations seen in
the signal was identified to be related to the heater's antenna pattern and to
the transmitted pulse shapes. Other observed variations can be related to the
spatial and temporal variations of the ionosphere and its different responses
to the used transmission frequencies and to the transmitted O- and X-wave
modes. Some trends in the observed signal may also be associated to changes in
the properties of ionospheric plasma resulting from the heater's
electromagnetic wave energy. This paper is, to authors' best knowledge, the
first observation of this kind of "self-absorption" measured from the
transionospheric signal path from a powerful radio source on the ground to the
satellite-borne receiver.
