  We proposed and analyzed a scheme to generate large-size Schr\"{o}dinger cat
states based on linear operations of Fock states and squeezed vacuum states and
conditional measurements. By conducting conditional measurements via photon
number detectors, two unbalanced Schr\"{o}dinger kitten states combined by a
beam splitter can be amplified to a large-size cat state with the same parity.
According to simulation results, two Schr\"{o}dinger odd kitten states of
$\beta=1.06$ and $\beta=1.11$ generated from one-photon-subtracted squeezed
vacuum states of $-$3 dB, are amplified to an odd cat state of $\beta=1.73$
with a fidelity of $F=99\%$. A large-size Schr\"{o}dinger odd cat state with
$\beta=2.51$ and $F=97.30\%$ is predicted when the input squeezed vacuum states
are increased to $-$5.91 dB. According to the analysis on the impacts of
experimental imperfections in practice, Schr\"{o}dinger odd cat states of
$\beta>2$ are available. A feasible configuration based on a quantum frequency
comb is developed to realize the large-size cat state generation scheme we
proposed.
