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Calibration of Spectrum Analyzer

Posted: Wednesday 15th Oct 2008, 20:50
by timrim
I am calibrating an Advantage Instruments ITC 1300C Spectrum Analyzer, I am calibrating the attenuator switch settings by injecting a known (Lab Standard) signal strength into the unit. My question is:

Would it make more sense to inject the proper amplitude signal and calibrate the attenuators at half scale or for top of scale reading?

Logic tells me half scale because I would think that the attenuator accuracy would be more accurate over the entire scale this way (top to bottom).

If I were to calibrate it for top of scale, it would seem that the lower scale readings would be further off.

Unfortunately, the manufacturer is no longer in business and the manual does not specify the proper procedure.

Here is an example of what I am talking about.

I have 4 attenuator switches and they are set up as follows:

+10dbm (full scale)
0dbm (full scale)
-10dbm (full scale)
-20dbm (full scale)

Since the scale is divided into 10 graticules (5 graticules = half), here is the signal levels that I used for calibration:

-30dbm = half scale
-40dbm = half scale
-50dbm = half scale
-60dbm = half scale

I hope I made that easy to follow.

Posted: Thursday 16th Oct 2008, 4:19
by The Defpom
Personally I would use the full scale calibration, and then verify the scale reading afterwards at lower levels to ensure that it is OK

Posted: Thursday 16th Oct 2008, 5:06
by timrim
They are off at the lower end, in fact, they are off about -8dbm, if I remember correctly. Also, when I calibrated it with top of scale, my 500mhz marker, which is calibrated at -60dbm, would not agree with a 500mhz -60dbm signal injected at front of analyzer. Now, they are pretty close.
You have me thinking though, because the attenuator buttons do represent top of scale. I may try it again for top of scale and see which way gives me the least error overall. There are errors either way, I am just trying to keep them as low as possible over the entire scale.