  Averaged pulse profiles of three nearby pulsars: B1929+10, J0437-4715 and
B0950+08 exhibit unusual `double notches'. These W-like looking features
consist of two adjacent V-shaped dips that approach each other at increasing
observation frequency nuobs roughly at a rate sep \propto nuobs^{-1/2}, where
sep is the separation between the notches' minima. We show that basic
properties of the notches, namely their W-like look and the rate of their
converging can be understood within a narrow class of models of coherent radio
emission from pulsars: the free electron maser models based on coherent inverse
Compton scattering of parallel oscillations of ambient electric field. The
observed properties of the pulsars imply that the Fourier spectrum of the
wiggler-like oscillations is narrow and that the broad-band character of the
radio emission reflects the width of the electron energy distribution. Such a
model provides a natural explanation for the frequency-independent separation
between the main pulse and interpulse of B0950+08 as well as for the lack of
radius to frequency mapping in the conal-like emission of J0437-4715. The
frequency behaviour of the main pulse in the profile of the first radio
magnetar XTE J1810-197 can also be explained within this model.
