We presented nineteen cases of zebra pattern structure (ZPS) and fiber bursts (FB) in four radio bursts at the frequency range about 3 GHz, using the new microwave spectrometer of NAOC between 2.6-3.8 GHz (China, Huairou station) with high resolution (10 MHz and 8 ms). FB and ZPS have about the same spectral parameters, and the main one - the frequency separation between the emission and the neighbouring low frequency absorption ∼30 MHz. Therefore we consider both fine structures as whistler manifestation. New calculations show an increase of the whistler growth rate with the increase of temperature near flare region, a decrease of electron cyclotron damping and a decrease of whistler frequency up to 0,1 of electron cyclotron frequency. The duration of fiber bursts about 2 sec corresponds to the whistler waves propagating undamped at about 2 sec, which requires the whistler increment <0,5 1/s. This finding is used to obtain the magnetic field strength in the generation region. For reasonable value of electron temperature (2-20 MK) B=125-190 G for regions, where the electron density is (8-18) × 10¹⁰ cm^-3.