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SFDR and Reference Level of Spectrum Analyzer (Read 12108 times)

ywguo

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Posts: 943
Shanghai, PRC

SFDR and Reference Level of Spectrum Analyzer
Nov 24^th, 2010, 10:05pm

Hi Guys,

When I measured a sine wave with spectrum analyzer. I am curious that the reference level impacts the harmonics. For ref level = 0 dBm, SFDR ≈ 72 dBc. For ref level = 10 dBm, SFDR ≈ 81 dB. I thought the reference level is used to adjust the display only. I am reading a few documents of Agilent about spectrum analyzer. However, I have not find the answer until now. Would you please comments this phenomina?

Best Regards,
Yawei

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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: SFDR and Reference Level of Spectrum Analyzer Reply #1 - Nov 24^th, 2010, 10:06pm Reference Level = 0 dBm
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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: SFDR and Reference Level of Spectrum Analyzer Reply #2 - Nov 24^th, 2010, 10:07pm Reference Level = 10 dBm
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currant

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Posts: 31

Re: SFDR and Reference Level of Spectrum Analyzer
Reply #3 - Nov 25^th, 2010, 12:22am

Hi, ywguo.
I think answer is simple. You overload internal circuits of spectrum analyzer (SA). As it can sees in your pictures, when You modify refLevel - value of internal attenuator also modify, and input signal attenuate before it come on SA's internal circuits. This is bad for noise (SNR) measurment, but good for HD measurment.

Best regards.

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ywguo Community Fellow Offline Posts: 943 Shanghai, PRC	Re: SFDR and Reference Level of Spectrum Analyzer Reply #4 - Nov 25^th, 2010, 7:42pm Hi Currant, I have not noticed the change of ATTN. Thanks Yawei
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rfidea Senior Member Offline Posts: 159 Europe	Re: SFDR and Reference Level of Spectrum Analyzer Reply #5 - Dec 31^st, 2010, 2:04am Hi, I agree with Currant. Changing the reflvl will change the internal signal level in the analyser, it does not only change the display. The spectrum analyser is a radio receiver! /ssahl
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