[en] The paper presents brightness temperatures of the supernova remnant HB 9 measured with the UTR-2 radio telescope at the frequencies from 12,6 to 25 MHz. The spectral index of the source below 1 GHz is 0,43±0,05. Below 30 MHz, th spectrum shows a drop due to absorption in ionized hydrogen around or within the remnant. The optical depth of the hydrogen is 0,05±0,03 at 25 MHz and the electron density is 0,8 cm^-3. The volume density of radiation in the shell is about 7,5x10^-37 erg/(cm³xsxHz) at 25 MHz and the magnetic field strength is roughly 2,5x10^-5 Oe. The total energy of relativistic particles and the magnetic field in the supernova remnant is about 10⁵⁰ erg