What are the units for an S11 measurement?

[egill]

I am controlling an HP 8753E Network Analyzer with a desktop running Labview 8.0 through a GPIB connection.  I am trying to measure S11 (reflected power from port 1), and when I open the file returned after running the Labview program, the magnitude of reflected power is in the 40 to 85 range (no units indicated).  However, when I make the same measurement manually and save it to disc, the units are in dBm and range from -4 to -31 dBm.

If I plot both files on top of each other, they match up exactly, so they are clearly correct, I just can't figure out what the units are in the file returned from the Labview program.  I tried converting the values from mW or microW into dBm, and that does not appear to be correct.  Does anyone know or have any thoughts about what units this might be in?  Thanks!

[smercurio_fc]

When running what LabVIEW program?

[egill]

Sorry, I am running the Hewlett-Packard / Agilent Technologies Agilent 87XX Series Signal Generator,Analyzer plug and play driver downloaded from the NI instrument website.

The units displayed directly from the instrument when operated from the front panel for log magnitude are actually dB, not dBm.

[Anthony_F]

Hello egill,

How are you setting up your S11 measurement? Can you describe the  hardware and how it is connected?  It would also be helpful if you could post pictures of both your front panel with the data returned and also your block diagram.