Author Topic: Phase Noise Head to Head: Siglent SSA3032X vs HP 8566B vs SignalHound SA124B  (Read 4564 times)

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Offline G0HZU

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I stuck in the numbers to ADI SIMPLL for the Zcomm VCO used for LO1 and the 703PLL chip and also a typical 10MHz reference and I got the PN response below for LO1:

This shows the noise contribution of all the major components in the first LO and the (hand drawn) green trace shows the 6dB degradation in phase noise due to the external doubler. I had to add this in by hand and it is the top 'Total' trace in ADI SIMPLL lifted by 6dB.

I chose a loop BW of 80kHz and an active loop filter using a low noise opamp and a phase detect frequency of 10MHz . But it may run the PD at a higher frequency than this. I'm just guessing but the results seem to agree with your plots at the lower end of the analyser range.

« Last Edit: June 01, 2018, 12:22:10 am by G0HZU »
 

Offline G0HZU

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Lowering the loop BW a bit and choosing a lower noise opamp (in the PLL filter) gets it closer? It would help if we knew the PD frequency and maybe a few other things. But the plot below shows a ballpark phase noise response using the same major parts as the LO1 design in the Siglent SSA.

« Last Edit: June 01, 2018, 12:31:11 am by G0HZU »
 

Offline hendorog

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Yes that is looking very close. Simulation matching reality!
 

Offline hendorog

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The cleanest regular analyser I have here for 100kHz offsets is my fairly ancient Advantest TR4172. It manages -128dBc/Hz at 100kHz offset across HF/VHF and up to 1GHz. The only spectrum analyser I have that beats the SignalHound at close offsets down at 20MHz is my 8GHz Tek RSA3408A. It beats it by maybe 15-20dB at offsets below 10kHz.

This might be of interest - I have been experimenting with 'reducing' the phase noise floor of the SignalHound.

The one which appears to work is NFE, basically just measuring the noise floor and subtracting it from the measurement - as described here: http://literature.cdn.keysight.com/litweb/pdf/5966-4008E.pdf

I have applied this to phase noise by measuring a very clean signal and then subtracting that trace from subsequent measurements. It provides about a 10dB improvement in the PN floor.

The process is basically:

Record baseline sweep of clean signal with averaging set to 1000. The Sig gen was set to Noise mode 1 which is its lowest PN mode.
Convert to dBc/Hz => dB - 17.5 for RBW of 100Hz
Convert to mW => 10 ^ (mW/10)
Call this baseline

Record actual measurement with averaging set to 1000 - I switched the noise mode of the Sig Gen to 'Normal' which is not as clean to provide the measurement.
Convert to dBc/Hz => dB - 17.5 for RBW of 100Hz
Convert to mW => 10 ^ (mW/10)
Call this mn

Calculate corrected value in mW => abs(m1 - baseline)
Convert to dBc/Hz => 10 * log(mW)
Call this mn_adjusted

Chart frequency offset vs mn_adjusted

Here is a google spreadsheet template which does this. It is view only, but you should be able to create a copy of this for yourself (File menu, Make a Copy) and then plug your own numbers into the Baseline and Measurement sheets. 

https://docs.google.com/spreadsheets/d/18VlzMaz6_csRroIl1bk0MpA9q1dbmOahmxpGaENg_uw/edit?usp=sharing


This image shows the results I got measuring the 2041 in Normal noise mode with and without this:
https://docs.google.com/spreadsheets/d/e/2PACX-1vRdEo1EnRjM5oINIitp9IARpjr7TZMN9ZJw90Clzg3Rpl_2rZZi9MDotEedda1psExLc_pL910KjQDz/pubchart?oid=680692226&format=interactive








 


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