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Zero response question

Posted: Mon Apr 02, 2012 6:20 pm
by William Dillon
Attachments :
  1. [url=file:///C:\Users\jose\AppData\Local\PG Offline 4\Attachments\spectrumanalyzer\zero hump.pdf t=_self]zero hump.pdf[/url]
[/list]Hi everyone,

Finally, my analyzer is coming together... It has been a long road, but I think I've got some results. Yesterday, I got it integrated such that I could run a zero response plot. My questions is related to the fact that it looks unlike any zero response that I've ever seen. For some background, I'm using the custom mac software that I've been working on for the last few months. To generate the plot, I'm executing a PLO1 sweep from 1013.0 to 1013.6 and the standard MSA topology. I've left the input to Mixer 1 open. This graph was 1000 steps with 100mS between each sample using the mid video filter and a 2kHz crystal filter. The 4 stage coaxial filter was used. I have no calibration functions available yet, so the dB scale is mostly meaningless. I'm using the idealized response from the datasheet, and it should be considered a dBc scale.

I can't figure why I'm getting those sidebands. Could it be a modulation issue? I'm not aware of any large amount of noise on the 20v supply, for example.

Has anyone seen anything like this? Ideas?


- Will