The changes of the helical pitch in antiferroelectric phase versus temperature were calculated based on measurements of selective reflection of the light in four homologous series CnF2n+1COO(CH2)(6)O-A-COOC* H(CH3)C6H13 (A-the rigid corePhCOOPhPh, PhPhCOOPh, PhPhCOO(F)Ph or PhPhCOOPh(F), Ph - phenyl ring, n is changed from 1 to 7). The values of helical pitch do not change in monotonous way with increase of the chain length. The even members have shorter pitches.