What happens when I set attenuation values in 5660 vis

[ness4]

Hello,

I am using the 5660 vis and I noticed that you can use auto attenuation or you can set your own attenuation values.  When I disable auto attenuation and try to set my own values I never see a difference in my SA display.  Is this correct behavior?

Thanks!

[Robert_F]

Hello ness4,

There would not be a noticeable difference in your measurement except for the noise floor. 

If you are acquiring a single tone at -10dBm into the 5660 and 10dB of attenuation is applied, then you would see a -10dBm tone on your graph.  The attenuation is applied before the mixer and the driver will then correct your tone accounting for that attenuation.   Without attenuation, the mixer will acquire a -10dBm tone. 

With 10dB of attenuation, the mixer would acquire a -20dBm tone.  The driver would then take that tone and account for the attenuation before the mixer.  Now you would see a -10dBm tone on your LabVIEW graph.

Depending on the attenuation that is applied, the noise floor will change.  This is the internal noise that is created by using the attenuators.

[ness4]

Thank you, Robert F!  Your reply was a GREAT help!

One more question... I'm wondering if there's some way that we can figure out what attenuation values are automatically used by the VIs.  We're analyzing the noise floor and so we'd like to factor in the auto-attenuation values when we run our algorithms!

Thanks!

[Robert_F]

Hello ness4,

The Auto mode sets the mixer level for you.

For all reference levels > -20dB, the mixer level gets set to -20dBm.
For all reference levels <=-20dB, the mixer level is equal to the reference level.

Basically, for reference levels >-20dB, the attenuation can be calculated using the formula in the attached screenshot.
For reference levels <=-20dB, the attenuation is set to 0.




Message Edited by Robert F on 01-02-2008 04:17 PM