  Since their discovery more than 50 years ago, broadband radio studies of
pulsars have generated a wealth of information about the underlying physics of
radio emission. In order to gain some further insights into this elusive
emission mechanism, we performed a multi-frequency study of two very well-known
pulsars, PSR~B0919+06 and PSR~B1859+07. These pulsars show peculiar radio
emission properties whereby the emission shifts to an earlier rotation phase
before returning to the nominal emission phase in a few tens of pulsar
rotations (also known as `swooshes'). We confirm the previous claim that the
emission during the swoosh is not necessarily absent at low frequencies and the
single pulses during a swoosh show varied behaviour at 220~MHz. We also confirm
that in PSR~B0919+06, the pulses during the swoosh show a chromatic dependence
of the maximum offset from the normal emission phase with the offset following
a consistent relationship with observing frequency. We also observe that the
flux density spectrum of the radio profile during the swoosh is inverted
compared to the normal emission. For PSR~B1859+07, we have discovered a new
mode of emission in the pulsar that is potentially quasi-periodic with a
different periodicity than is seen in its swooshes. We invoke an emission model
previously proposed in the literature and show that this simple model can
explain the macroscopic observed characteristics in both pulsars. We also argue
that pulsars that exhibit similar variability on short timescales may have the
same underlying emission mechanism.
