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SFDR and Reference Level of Spectrum Analyzer (Read 10307 times)
ywguo
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SFDR and Reference Level of Spectrum Analyzer
Nov 24th, 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
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Re: SFDR and Reference Level of Spectrum Analyzer
Reply #1 - Nov 24th, 2010, 10:06pm
 
Reference Level = 0 dBm
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Fs_50M_XTAL_CLK_Fin_480kHz_EVAL_0dBm_REF.GIF
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ywguo
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Re: SFDR and Reference Level of Spectrum Analyzer
Reply #2 - Nov 24th, 2010, 10:07pm
 
Reference Level = 10 dBm
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Fs_50M_XTAL_CLK_Fin_480kHz_EVAL_10dBm_REF.GIF
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currant
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Re: SFDR and Reference Level of Spectrum Analyzer
Reply #3 - Nov 25th, 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.

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ywguo
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Re: SFDR and Reference Level of Spectrum Analyzer
Reply #4 - Nov 25th, 2010, 7:42pm
 
Hi Currant,

I have not noticed the change of ATTN.


Thanks
Yawei
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« Last Edit: Nov 26th, 2010, 2:30am by ywguo »  
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rfidea
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Re: SFDR and Reference Level of Spectrum Analyzer
Reply #5 - Dec 31st, 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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