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We analyze the possibilities of detecting a signal in the hydrogen 21 cm line, which was formed in the early universe during the Dark Ages, using the Ukrainian radio telescopes UTR-2 and GURT of the National Academy of Sciences of Ukraine. As a result of cosmological expansion, this line is shifted to the decameter range of wavelengths (λobs ≈ 18 m, νobs ≈ 16 MHz) and is in the band of operating frequencies of these telescopes. The brightness temperature of the predicted sky-averaged global signal ranges from ∼ −0.08 to ∼ 0.02 K, depending on the cosmological model. Such a weak signal is a big challenge even for the world's largest radio telescope in the decameter wavelength range UTR-2, since the signal level of the synchrotron radiation of the Galaxy at these frequencies is 20 000-40 000 K. The paper highlights the peculiarities of spectroscopy at decameter waves, interfering factors of natural and instrumental origin and ways to eliminate them in order to reliably detect the signal in the 21 cm line, which can become an important source of information both about the environment in which the first stars and galaxies were born, and about the nature of dark matter particles and the magnitude of primordial magnetic fields. It was concluded that the detection of such a signal using the most sensitive radio telescopes of the decameter wavelength range is quite possible (with a frequency accumulation of 25 MHz, the detection time will be ∼ 50 days) and can be implemented in the coming years of peace in Ukraine. [ABSTRACT FROM AUTHOR]