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The results of spectral index mapping of the quasar 3C345 are presented. Three VLBI maps of the quasar were obtained at 1.3~(June~92), 3.6~(September~92), and 6cm~(June~92). The spectral index maps were produced in AIPS by comparison pairs at adjacent wavelengths: 1.3cm $\iff$ 3.6cm; 3.6cm $\iff$ 6cm. Because of the high dynamic range of the given VLBI maps, it is possible to probe spectral index distribution along and across the jet, up to $\approx$10 \rm mas away from the core. This shows a flatter spectrum in the places of bright component locations, along with a steepening toward the jet limbs. Zero spectral index in the core might be considered as an independent size indicator, allowing to determine the core size, the knowledge of which is essential for cosmology related studies. In addition to mapping, we calculated the components spectral indices, using the component fluxes obtained from model fitting to the data. Using two spectral indices taken with different frequency combinations, it is possible to estimate the shape of the synchrotron spectrum of the core or bright components. The obtained spectra of the bright components show significant evolution of the emission with increasing distance from the core.
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