In the absence of decoherence the magnetisation is not dependent on the inter-pulse delay, 𝜏. In a DFHE experiment coherences and echoes are generated on both spins, and the application of 180° pulses at time 𝜏 prevents complete refocussing of the inter-spin coupling term. As a result, the echoes are modulated by the inter-pulse delay with frequency 𝜔 )* :