function freq_write_bin, master_bin,output_bin, $
                         time_mark, freq_mark, freq_data, debug=debug

;modified by G. Burgess 11/6/2001  for 'freq' and 'freq_mark'
!quiet = 1  ; turn off message

  infile = master_bin
  unit1 = 1
  unit2 = 2
  openr, unit1, infile   ;, /get_lun
  openw, unit2, output_bin  ;,  /get_lun

  firstbyte = lonarr(1)
  lastbyte = lonarr(1)

; read and write the header record

  header = lonarr(40)
  readu,  unit1,firstbyte,header,lastbyte
  writeu, unit2,firstbyte,header,lastbyte

; read and write the frequency marker records

  freq_time = dblarr(2)

  for j=0, 21 do begin
    readu,  unit1, firstbyte, freq_time, lastbyte
    freq_time[0] = freq_mark[j]
    freq_time[1] = time_mark[j] * 1000.0
    freq_time = swap_endian(freq_time)
    writeu, unit2, firstbyte, freq_time, lastbyte
  endfor

; read and write the number of colums and rows

  column_row = {col: 1L, row: 1L}
  readu,  unit1, firstbyte, column_row, lastbyte
  writeu, unit2, firstbyte, column_row, lastbyte

  column_row = swap_endian(column_row)

; read and write the delay time and apparant range

    time_range = dblarr(column_row.row)
    readu,  unit1, firstbyte, time_range, lastbyte
    writeu, unit2, firstbyte, time_range, lastbyte

    appar_range = dblarr(column_row.row)
    readu,  unit1, firstbyte, appar_range, lastbyte
    writeu, unit2, firstbyte, appar_range, lastbyte

; read and print the ionogram
  ionogram = {d: dblarr(2), b: bytarr(column_row.row)}
  freq_iono = dblarr(column_row.col)
  time_iono = dblarr(column_row.col)
  isis = bytarr(column_row.col, column_row.row)
  for i = 0, column_row.col-1 do begin
    readu,  unit1, firstbyte, ionogram, lastbyte
    ionogram = swap_endian(ionogram)
   ; time_iono(i) = ionogram.d(0)
   ; freq_iono(i) = ionogram.d(1)
   ; for j = 0, column_row.row-1 do isis(i, j) = ionogram.b(j)
    freq_iono(i) = freq_data(i)
    ionogram.d(1) = freq_iono(i)
    ionogram = swap_endian(ionogram)
    writeu, unit2, firstbyte, ionogram, lastbyte
  endfor

  close,unit1
  close,unit2


!quiet = 0; turn messages back on
return, 1
end