high power noise level on 5660

[StoneAntony]

Hi, I'm working on 5660 RF signal anlyzer and i notice the high power noise level when full-span range frequency is turn-on (-55dBm with ref. level 0dBm and -80dBm with ref.level -20dBm Attenuation 0 dB RBW type = 3dB) . I would like to know if this is due to hardware...

Thanks.

[Andy_Hinde]

Hello,
The displayed noise floor is a function of noise density, RF attenuation, and Resolution Bandwidth.

Noise Floor (dBm) = Noise  Density (dBm/Hz) + RF Attenuation (dB) + Log10 (RBW)

RF Attenuation = Ref Level (dBm) - Mixer Level (dBm)

The mixer level is typically set to -20 dBm for reference levels >= -20 dBm. When the ref level is lowered below -20 dBm, the mixer level is lowered with it essentially maintaining 0 dB attenuation.

To check your PXI-5660 performance, I recommend setting the span <= 20 MHz, the reference level to -30 dBm, and the RBW to 1 kHz or 10 kHz. Check the expected noise floor against the noise floor you see. The noise density values are in the PXI-5660 specs and vary based on RF tuned center frequency. If you are seeing unexpected behavior, an uploaded screenshot will help greatly.

Regards,
Andy Hinde
National Instruments