      SUBROUTINE FRTIME(F1,TIME)
C     SUBROUTINE FRTIME. COMPUTE GMT (DECIMAL HRS) AT WHICH FA OCCURRED
C     FROM THE SWEEP RATE OF THE SATELLITE. INITIAL FREQUENCY F1
C     OCCURRED AT TIME GMT1 (IN DECIMAL HOURS).
C     ISAT IDENTIFIES THE SATELLITE: 1=AL-1; 2=AL-2; 3=ISIS-1; 4=ISIS-2.
C     REFERENCE TIMES AT FREQUENCIES FBR ARE STORED, FOR EACH SATELLITE,
C     IN THE ARRAY REF. THESE ARE BASED ON THE FOLLOWING SWEEP RATES:
C     ALOUETTE-1: SWEEP RATE = 1.0 MHZ/SEC (0.5-12 MHZ).
C     ALOUETTE-2: SWEEP RATE = 0.125 MHZ/SEC (0.2-2 MHZ); =1 (2-15 MHZ).
C     ISIS-1: SWEEP RATE = 0.31 MHZ/SEC (.25-2 MHZ); = 0.88 (2-5 MHZ);
C                        = 1.03 (5-20 MHZ).
C     ISIS-2: SWEEP RATE = 0.375 MHZ/SEC(.25-2 MHZ); = 1.125 (2-5 MHZ);
C                        = 1.50 (5-20 MHZ).
      IMPLICIT REAL*8(A-H,O-Z)
      COMMON /MISC/ DP,FH1,ASUM,BSUM,FA,CPH,X1,X2,GMT1
      COMMON /SWJTCH/ ISAT,LOCSAT,IFXS,NCASES,ICODE(4),N,METHOD,IORD,IP
      REAL*8 FBR(4)/0.,2.,5.,20./,  REF(16)/0.,2.,5.,20.,0.,16.,19.,34.,
     R  0.,6.45,9.86,24.41,0.,5.34,8.,18./,  REFT(4)
      K=4*(ISAT-1)
      DO 100 I=1,4
  100 REFT(I)=REF(K+I)
      DELT=TAB(FBR,REFT,4,1,FA)-TAB(FBR,REFT,4,1,F1)
      TIME=GMT1+DELT/3.6D3
      RETURN
      END
