psi functions permits a spaceship to assume a psuedo-velocity (not a true speed in the mechanical sense) limited only by the frequency of the engine's oscillators."
-Poul Anderson, Virgin Planet (London, 1966), "Author's Note," pp. 150-156 AT p. 150.
(These psi functions are not connected with ESP.)
Another Means Of FTL
STL Or FTL?
Alternative Quantum Mechanics
This "phase velocity" FTL in Anderson's Psychotechnic History differs from the "quantum jump" FTL in his Technic History although there are similar references to "psuedo-velocity" and to oscillator frequencies.
In James Blish's pantropy series, Okie series and The Quincunx Of Time, modulated phase velocity is used to send messages faster than light along a connecting beam of light-speed radiation. The Okies also have the instantaneous Dirac transmitter and the Service in Quincunx additionally has an application of the Dirac that enables reception of messages from the past and future as well as the present.
In Poul Anderson's "Time Patrol," both instantaneous travel and time travel require infinitely discontinuous functions. Thus, there are conceptual connections between several series.