text:       SUBROUTINE EXCSD(Q,Z,KEY,NSTEP,HEXTTL,AOPT)
  C
        IMPLICIT REAL*8 (A-H,O-Z)
  C
  C    *****************************************************************
  C    *                                                               *
  C    *   THIS IS A CSC EXECUTIVE ROUTINE FOR FAST FOURIER TRANSFORM  *
  C    *   ANALYSIS. MODIFIED TO CHANGE CALLING SEQUENCE SEPT. 1977.   *
  C    *                                                               *
  C    *****************************************************************
  C
        COMPLEX*16 HEXTTL,AOPT
        COMPLEX*8    Z(1025),ZSTORE(1025)
        REAL*4 DELT, Q(2050),QSTORE(2050),DUMMY(7)
  C     EQUIVALENCE (Q(1),Z(1))
        COMMON/RMAIN1/DELTAT,FACTOR,FREQ,TSTOP,DELMIT
        WRITE(6,937)
   937  FORMAT(1H1)
        WRITE(6,938)
   938  FORMAT(' ********************************     FAST    FOURIER
       1 TRANSFORM    ANALYSIS    ***********************')
  C
        WRITE(6,600) KEY
    600 FORMAT(/,20X,'&&&&    FOR KEY =',I3,/)
  C
        WRITE(6,6000) HEXTTL,AOPT
   6000 FORMAT('0',5X,10('*'),5X,'DATA RELATED TO ',2A8,2A8,' PLOT',5X,
       *       10('*'),/)
  C
  C
        WRITE(6,625) NSTEP
    625 FORMAT(/,20X,'NO. OF POINTS =',I4,/)
  C
        NHALF=(NSTEP+1)/2
        DELT=FREQ
        DO 201 I=1,NHALF
    201 ZSTORE(I)=Z(I)
        DO 301 I=1,NSTEP
    301 QSTORE(I)=Q(I)
        CALL CSD(Z,Q,NSTEP,NHALF,IWIN,DELT,DUMMY)
        DO 202 I=1,NHALF
    202 Z(I)=ZSTORE(I)
        DO 302 I=1,NSTEP
    302 Q(I)=QSTORE(I)
     15 CONTINUE
        RETURN
        END
  