Ok, so I've made some progress with this.
Firstly - getting the frequencies with the decimal correct : I used this macro in excel.
------------------------
Sub doit()
Dim c As Range
For Each c In Range(ActiveCell, ActiveCell.End(xlDown))
If Len(c) > 3 Then
c.Value = Left(c, 3) & "." & Mid(c, 4)
End If
Next
End Sub
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Secondly - I had to use text to columns in excel to separate the two values
Now, for the RF level. As it says in the header of the exported WSM .csv file:
RFUnit;dB
So.. it's in dB as opposed to dBm and there doesn't seem to be an option within WSM to change units on the exported .csv file. I'm able to import the sweep data into IAS now, but because it's in dB the scale is incorrect. Next to get that that fixed, just need to find out what reference power they are using for the dB value.