Hi Andrew,
Thanks for your post above, and I apologize for the change in login name — I forgot my password. I’m going to walk through what I understand so far, and hopefully you can help me pick up the pieces after that.
In the case above with decimation of 32, this implies a sample rate of 40 MS/sec / 32 = 1.25MS/sec as shown on the GUI, and therefore the bandwidth of the spectrum shown is 1.25 MHz. You’ve applied a filter and Blackman windowed the data, which results in the rolloff we see in the spectrum window.
So: decimation controls the sampling rate, and the “IF Bandwidth” control in zero span mode controls the filter cutoff points, if I’m understanding things correctly. Question 1: Is this same filtering applied to the raw I and Q data recorded in the .iq files?
In the case above, we’ve chosen IF bandwidth of 1 MHz, so this is controlling the 6 dB down points of said filter… if we are only controlling the 6 dB down points, the effective noise bandwidth (ENBW) of this filter must be somewhat greater than 1 MHz, correct? Question 2: how much greater, and how can I determine/estimate the filter ENBW based on the description of the windowed filter you’re using?
I’ve looked a lot of places trying to find the ENBW for the combination of window and filter you’re using, but typically I find references to the resolution bandwidth of spectrum analyzers and so on, and I’m not sure these are really applicable to the ENBW for an IQ recording. An example is this page.
We’re using a calibrated noise source to assess our system gain and noise figure, but until we have a handle on ENBW for the BB60C, we’re floundering a bit. Any help/discussion would be appreciated.