Emission altitude in radio pulsars
  This paper presents a method of estimation of emission altitudes using observational data - precise measurements of pulse profile widths at low intensity level. The analysis of emission altitudes obtained using this method for a large number of pulsars gives constraints that should be useful for theory of coherent pulsar emission. It seems that radio emission originates at altitudes of about few percent of the light cylinder and that they depend on frequency, pulsar period and period derivative. 
J. Kijak