  The source-frequency phase-referencing (SFPR) technique has been demonstrated
to have great advantages for mm-VLBI observations. By implementing simultaneous
multi-frequency receiving systems on the next generation Event Horizon
Telescope (ngEHT) antennas, it is feasible to carry out a frequency phase
transfer (FPT) which could calibrate the non-dispersive propagation errors and
significantly increase the phase coherence in the visibility data. Such
increase offers an efficient approach for weak source or structure detection.
SFPR also makes it possible for high precision astrometry, including the
core-shift measurements up to sub-mm wavelengths for Sgr A* and M87* etc. We
also briefly discuss the technical and scheduling considerations for future
SFPR observations with the ngEHT.
