  In the interplanetary space solar wind plasma, whistler waves are observed in
a wide range of heliocentric distance (from ~20 solar radii (RS) to Jupiter's
orbit). They are known to interact with solar wind suprathermal electrons
(strahl and halo) and to regulate the solar wind heat flux through scattering
the strahl electrons. We present the results of applying the technique to
determine the whistler wave propagation direction to the spectral data
continuously collected by the FIELDS instruments aboard Parker Solar Probe
(PSP). The technique was validated based on the results obtained from burst
mode magnetic and electric field waveform data collected during Encounter 1. We
estimated the effective length of the PSP electric field antennas (EFI) for a
variety of solar wind conditions in the whistler wave frequency range and
utilized these estimates for determining the whistler wave properties during
PSP Encounters 1-11. Our findings show that (1) the enhancement of the whistler
wave occurrence rate and wave amplitudes observed between 25-35 RS is
predominantly due to the sunward propagating whistler waves population
associated with the switchback-related magnetic dips; (2) the anti-sunward or
counter-propagating cases are observed at 30-40 RS; (3) between 40-50 RS,
sunward and anti-sunward whistlers are observed with comparable occurrence
rates; and (4) almost no sunward or counter-propagating whistlers were observed
at heliocentric distances above 50 RS.
