VBA Loop until blank cell

The below coding works and carries on looping but i need it to stop when it reaches a blank cell in B column in Sheet1.

Sub test()
Do
  ActiveCell.FormulaR1C1 = "=""TTG""&Sheet1!R[1]C[2]"
  ActiveCell.Offset(1, 0).Select
Loop
End Sub

I tried the below but not sure if on right track.

Sub test()
Range("B1").Select
Do Until ActiveCell.Offset(, 2) = ""
        ActiveCell.FormulaR1C1 = "=""TTG""&Sheet1!R[1]C[2]"
        ActiveCell.Offset(1, 0).Select
Loop
End Sub