  In this paper, we presented a detailed single pulse and polarization study of
PSR J0614+2229 based on the archived data observed on 2019 August 15 (MJD
58710) and September 12 (MJD 58738) using the Ultra-wideband Low-frequency
Receiver on the Parkes radio telescope. The single-pulse sequences show that
this pulsar switches between two emission states, in which the emission of
state A occurs earlier than that of state B in pulse longitude. We found that
the variation in relative brightness between the two states is related to time
and both states follow a simple power law very well. Based on the phase-aligned
multi-frequency profiles, we found that there is a significant difference in
the distributions of spectral index across the emission regions of the two
states. Furthermore, we obtained the emission height evolution for the two
emission states and found that, at a fixed frequency, the emission height of
state A is higher than that of state B. What is even more interesting is that
the emission heights of both states A and B have not changed with frequency.
Our results suggest that the mode switching of this pulsar is possibly caused
by changes in the emission heights that alter the distributions of spectral
index across the emission regions of states A and B resulting in the
frequency-dependent behaviors, i.e., intensity and pulse width.
