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Hello,
We are trying to recreate programmatically the Channel Power available in Spike via the SDK and we’re always coming off the value in Spike by about 5-6 dB (always higher).
We use the dBm formula found here (also attached): http://uniteng.com/index.php/2013/07/26/channel-power-measurements/
Question #1: is there a programatical way in SA_SWEEPING mode to get access to the channel power?
Question #2: if not, could you please confirm if you use the attached formula in Spike to calculate channel power? And if you don’t, would you have a suggestion for us to get the same results?
Question #3: unrelated, but is there a reason why the Bandwidth RBW doesn’t provide the expected points? Example: for a 1.2MHz span with 1kHz RBW, I would expect 1200 points, but I get 5058 points.
Thank you in advance.
Eric,
(Edit: after looking at the equation you linked, it looks like it accounts for the spectral window and the discrepancy is probably just the spur reject setting, leaving the full reply)
A couple things that come to mind regarding your measurement discrepancy. The SA44B has spur reject processing enabled by default. Unless you either disable this in the settings file menu or lower your VBW substantially, this will contribute to a lot of your error. Additionally you will want to account for the window bandwidth. All spectrum analyzers will utilize a spectral window. In our software this is the RBW shape control. By default, we use the flat top window. The spectral windows will also contribute to the calculation. Below I linked another thread which goes into detail regarding this and also you will find a code snippet in one of my replies which has the channel power code calculation from Spike. You can compare your code to it.
The spectral window is also why you are seeing a different sweep size than you expect. When using a spectral window, larger FFT sizes are required to achieve the same RBW, thus the larger sweep size. If you are unfamiliar with these window functions, see the other link below.
If you have follow up questions, please let me know.
https://signalhound.com/support/forums/topic/noise-bandwidth-of-resolution-bandwidth-filter/
https://en.wikipedia.org/wiki/Window_function
Regards,
Andrew
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