Hello. I used a HP 8565B signal generator, NIPXI 8650, and the RFSG (5421(5619).

[Matt_Lowe]

Hello. I used a HP 8565B signal generator, NIPXI 8650, and the RFSG (5421(5619).

Set at 450MHz with a power level of 0dBm.

I connected the output to the RFSA and looked at the power spectrum.

With each generator I noticed the other frequency bouncing around but the 450MHZ stayed constant.

The frequency wasn't always there so I had to turn up the averaging on the RFSA so it would stay long enough to take a screen shot.

One thing I did notice is with the resolution bandwidth set at 100K the second frequency was present and fluctuating. When I set the resolution bandwidth to 10K the second frequency disappeared and only the 450MHZ I had set the generator to was present.

[Raajit_Lall]

Resolution bandwidth determines the bin size of the FFT.  It is the smallest frequency that can be resolved in the bin.  These graphs show the same signal with varying resolution bandwidth.



As you can see the smaller the bandwidth the noise floor gets lower.  This also increases the acquisition time though.  The resolution bandwidth is inversely proportional to the number of samples being acquired.  By taking more samples in the time domain, or making the acquisition time longer while keeping the sampling rate the same, the resolution bandwidth is lowered.

If the acquisiton time is not of utmost importance to you, I would suggest keeping the RBW (Resolution Bandwidth) at the lower value since that will give you a cleaner signal and reduce the noise floor.

Hope I answered your questions.

Regards,

Message Edited by Raajit L on 01-29-2008 11:07 AM

[Matt_Lowe]

Thank you

that helped out alot.