  The magnetospheric locations of pulsar radio emission region are not well
known. The actual form of the so--called radius--to--frequency mapping should
be reflected in the aberration--retardation (A/R) effects that shift and/or
delay the photons depending on the emission height in the magnetosphere. Recent
studies suggest that in a handful of pulsars the A/R effect can be discerned
w.r.t the peak of the central core emission region. To verify these effects in
an ensemble of pulsars we launched a project analysing multi--frequency total
intensity pulsar profiles obtained from the new observations from the Giant
Meterwave Radio Telescope (GMRT), Arecibo Observatory (AO) and archival
European Pulsar Network (EPN) data. For all these profiles we measure the shift
of the outer cone components with respect to the core component which is
necessary for establishing the A/R effect. Within our sample of 23 pulsars 7
show the A/R effects, 12 of them (doubtful cases) show a tendency towards this
effect, while the remaining 4 are obvious counter examples. The
counter--examples and doubtful cases may arise from uncertainties in
determination of the location of the meridional plane and/or the core emission
component. It hence appears that the A/R effects are likely to operate in most
pulsars from our sample. We conclude that in cases where those effects are
present the core emission has to originate below the conal emission region.
