Currently our company is evaluating the new MXA and after some short testing, we found some internal spurs showed up in low frequency under FFT mode. (ie. center 15.4Mhz, span 25Mhz, RBW 1k, FFT 25Mhz). Our experiment was done with terminator, and the spurs are at least 10db higher noise floor. (the case above is not the worst case, we saw more serious ones) We double checked with VSA connected with MXA and turned out the same result. Also, the spurs will change in some frequency pattern when changing the center. So it is more like internal LO mixing product. However that did not happen on Sweeping mode.
The initial response from local representatives stating that this is not a issue and claim the MXA in FFT mode only reach -100dbm. Maybe I am wrong, but someone can show me why an internal spurs is not an issue, and where the -100dbm comes from.
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The initial response from local representatives stating that this is not a issue and claim the MXA in FFT mode only reach -100dbm. Maybe I am wrong, but someone can show me why an internal spurs is not an issue, and where the -100dbm comes from.
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I set up this measurement just as you specified: center 15.4Mhz, span 25Mhz, RBW 1k, FFT 25Mhz. While I noticed a spur at 15.8 MHz, it was at -115 dBm, which is 15 dB below the MXA's residual response specification of -100 dBm. There could be a number of things causing this including mixing products, something in the ADC, etc. Regardless, this spur is still within the guaranteed specification of the MXA (see page 38 of the MXA specs guide: You can find this by going to the Agilent web page and searching for MXA, and then clicking the product library Tab).
Also, I found that if I changed the span to 5 MHz or changed the center frequency to 16 MHz, the spur went away, giving me a nice clean noise floor.
-Mike