The DQCP condition with ωH ~ 0.75ωr requires 𝜔 𝑋 = √3 2 |𝑠 𝑛 |𝜔 1 ~0.25𝜔 𝑟 for CP to the STs. The scaling factor |sn| varies among the crystallites in powder samples affecting the HH CP matching condition. A ramp of the 1 H rf field was applied to compensate the mismatch . Fig. shows the 35 Cl rf power calibration profiles for 1 H → 35 Cl → 1 H double CP via the CT and STs. The comparison clearly shows much higher rf power are necessary for the STs to make up for the scaling of the effective rf field. In addition, the matching profile is much broader than for the CT because of the distribution of the scaling factor |sn| for powder samples similar to the broadening of the CP matching profile from inhomogeneous rf fields. Ramping the 1 H rf field helps to compensate the mismatch, nevertheless the spread of the amplitude of the effective rf field still makes the CP less efficient, being the main cause to the ~50% ST signal compared with the CT signal in Fig. . 35 Cl rf field amplitude B1/2π with a fixed 1 H ω1 ~0.75ωr. The transmitter offset was set near the 35 Cl CT for the black curve and increased by +180 kHz for the red curve. Fig. shows an overlay of 2D 1 H/ 35 Cl HETCOR spectra of hist with the double CP conditions discussed above for the CT and STs. The magic-angle setting was carefully calibrated such that the large first-order quadrupolar coupling is averaged with rotor synchronized t1 evolution . Only the isotropic and fourth-ranked second-order quadrupolar terms remain under MAS. For the spin S = 3/2 35 Cl nuclei, the ratios of the isotropic and fourth-ranked terms between STs and CT are -2 and -8/9, respectively . By measuring the separation between STs and CT peaks, the chemical shift position can be determined from the -2 ratio for the isotropic quadrupolar shift between STs and CT. The spectra in Fig. shows that the peaks from the STs and CT have similar width and are close to mirror images of each other as expected from the -8/9 ratio of their fourth-ranked terms. Acquisition of both CT and ST peaks allows for the separation of isotropic chemical and quadrupolar shift without the need of line shape fitting.