Excitation of HF axial magnetic field by axial HF current (f=50 MHz) is investigated in the coaxial waveguide under the weak external axial field (/spl les/1.5 Oe). The gyrotropic sample-amorphous Co-based wire (15 /spl mu/m in radius) serves as the central conductor of the wave-guide. Coefficient of energy transformation reaches magnitudes of the order of tens percent and is highly sensitive to external field due to the manifestation of the GMI-effect.