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Measurements >> RF Measurements >> SFDR and Reference Level of Spectrum Analyzer
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Message started by ywguo on Nov 24th, 2010, 10:05pm

Title: SFDR and Reference Level of Spectrum Analyzer
Post by ywguo on 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

Title: Re: SFDR and Reference Level of Spectrum Analyzer
Post by ywguo on Nov 24th, 2010, 10:06pm

Reference Level = 0 dBm

Title: Re: SFDR and Reference Level of Spectrum Analyzer
Post by ywguo on Nov 24th, 2010, 10:07pm

Reference Level = 10 dBm

Title: Re: SFDR and Reference Level of Spectrum Analyzer
Post by currant on 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.

Best regards.

Title: Re: SFDR and Reference Level of Spectrum Analyzer
Post by ywguo on Nov 25th, 2010, 7:42pm

Hi Currant,

I have not noticed the change of ATTN.


Thanks
Yawei

Title: Re: SFDR and Reference Level of Spectrum Analyzer
Post by ssahl on 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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