I am using com port 1 to read continious string of data at baud rate 4800,n,8,1 form a serial device

What can I do to detect a certain start of the string from this devise so that I can then manuplate the rest of the string. The start of the string in chr$(&H2).(hexi 02)

I tried the following:
Do
' DoEvents
Dim instring As String
Loop Until MSComm1.Input = Chr$(h2)
instring = MSComm1.Input

this doesnt work...