  The mode switching phenomenon of PSR J0614+2229 was studied by using the
archived observations at 686, 1369 and 3100 MHz with the Parkes radio telescope
which have not been published before, and combining existing observations from
the literature. Over a wide frequency range from 327 to 3100 MHz, the pulsar
switches between one mode occurring earlier in pulse phase (mode A) and the
other mode appearing later in phase (mode B), with a generally stable phase
offset between their profile peaks. The two modes are found to be different in
the following aspects. (1) Mode A has a flatter spectrum than mode B, with a
difference in the spectral index of about 0.5. This accounts for the phenomenon
that the flux ratio between the modes A and B increases with frequency, and
mode A becomes stronger than mode B above $\sim500$ MHz. (2) For mode B, the
flux density of the subintegrated profile is anticorrelated with the emission
phase, indicating that the emission from earlier phases is relatively stronger
than that from later phases; such an anticorrelation is not observed in mode A.
(3) The frequency dependence of the FWHM of the two modes are opposite each
other; namely, the FWHM of mode A increases with frequency, while that of mode
B decreases with frequency. A possible interpretation is suggested that the
longitudinal spectral variation across the two beams may be opposite each
other.
