Without the phase cycling proposed by E. Oldfield's group, the interpulse delay tau2 should be twice the duration of the central transition FID to observe the echoes. As a result, the echo amplitudes become small due to the spin-spin relaxation. Thank to this phase cycling, tau2 can be as short as the duration of the central transition FID.
Hahn echo sequence with this phase cycling also cancels the spurious signals such as the ringing generated by the nmr probe head or the signals from piezo electric materials in single crystal.
PROT F1 F2 XT ; protect all channels START, D1 [F1 @PLS1 RGATE] ; the first-pulse duration p1 D6 [ RGATE] ; spacing between pulses VD [F1 @PLS2 RGATE] ; the second-pulse duration p2 D7 [STA RGATE] ; acquisition delay AQ ; acquisition D0 ; recycle duration 1M ++PLS1 ; increment p1 pulse phase ++PLS2 ; increment p2 pulse phase GOTO START BEGIN LISTS PLS1, x x x x y y y y -x -x -x -x -y -y -y -y PLS2, x -x y -y x -x y -y x -x y -y x -x y -y RLS, x x -x -x -y -y y y -x -x x x y y -y -y END LISTS ; RECEIVER MODE: RPN ; TRIGGER MODE: NT