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Old 13th December 2012, 07:53 PM   #1131
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by dimitri View Post
AP internal oscillator
so thier spec is for the whole deal; source and analyzer, together, I would suppose? Or does the total sum of the harmonics shown = thier spec number? Thx. RNMarsh
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Old 13th December 2012, 08:12 PM   #1132
dimitri is offline dimitri  United States
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Richard, they specify THD+N in 22kHz bandwidth:
Analog generator residual THD+N At 1 kHz _(0.00025% + 1.0 μV) [–112 dB], 22 kHz BW
Analog analyzer Residual THD+N: At 1 kHz _(0.00025% + 1.0 μV) [–112 dB], 22 kHz BW
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Old 14th December 2012, 02:08 AM   #1133
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Yes. OK, I can see that. Then, I still need much better performance from these analyzers by one more zero. But that may not be possible? Thx-RNMarsh

Last edited by RNMarsh; 14th December 2012 at 02:11 AM.
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Old 14th December 2012, 04:43 AM   #1134
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Richard, you never made clear the frequency range of interest for you -- what resolution at what max freq. do you want to see?
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Old 14th December 2012, 06:05 AM   #1135
RNMarsh is offline RNMarsh  United States
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I'd like to see what existing/future designs can do, so being about 20dB better would give some semblence of accuracy; So around -130/-140 thd+n over 20Khz bw. Or better. Thx-RNMarsh
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Old 14th December 2012, 06:18 AM   #1136
RNMarsh is offline RNMarsh  United States
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Default 339A Residuals -

Using 339A analyzer - here is where the HP339A source residual is at (1KHz) [full scale is -80. 10dB/div]:
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Last edited by RNMarsh; 14th December 2012 at 06:23 AM.
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Old 14th December 2012, 06:48 AM   #1137
richiem is offline richiem  United States
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Well, the EMU 0204 and the QuantAsylum 400 ADCs, used with spectrum analysis software, can both do -140dBV or better noise floors, RE 1VRMS input, out to about 30kHz, but then both show a rising slope due to the noise shaping ADCs out to the 90kHz limit, when 192kHz sampling is used.

As I've mentioned, I use an Active Twin-T filter to notch the fundamental out of the way of the ADCs. I've also used it as a front end for my Tek 7L5 with good results. The self-distortion of the Active Twin-T is unknown to me at this point, but I have reason to believe all of its products are below -135dBV RE 1VRMS input. The Twin-T has metal film resistors, wirewound pots, and polyester caps at this point.

I'm very impressed with what you and David have gotten from the 339A -- it's nice to have a single unit for source and analysis that gives dependable results, and your 2ppm result is pretty darn good. I look forward to tackling my 339 after the first of the year, tho it may be quite a while after.
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Old 14th December 2012, 04:17 PM   #1138
klewis is online now klewis  United States
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Quote:
Originally Posted by RNMarsh View Post
I'd like to see what existing/future designs can do, so being about 20dB better would give some semblence of accuracy; So around -130/-140 thd+n over 20Khz bw. Or better. Thx-RNMarsh
Have a look at my post #772 in this thread. Using the Jim Williams super oscillator through Dick's active twin T with the HP3562A. I can see out to 100kHz with a noise floor around -135db. Also note that the oscilator output in these examples is at about 1.4vrms.

Ken
Please ignore the THD values in the aforementioned post. It's calculated by an HP8903a. I usually hand calc the THD.

Last edited by klewis; 14th December 2012 at 04:19 PM.
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Old 14th December 2012, 05:57 PM   #1139
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Quote:
Well, the EMU 0204 and the QuantAsylum 400 ADCs, used with spectrum analysis software, can both do -140 dBV or better noise floors.
Quote:
I can see out to 100 kHz with a noise floor around -135 dB.
He wants -130/-140 dB THD+N. Using large FFTs to move noise into even smaller bins doesn't help at all for THD+N...

Samuel
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Old 14th December 2012, 06:25 PM   #1140
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Quote:
Originally Posted by Samuel Groner View Post
He wants -130/-140 dB THD+N. Using large FFTs to move noise into even smaller bins doesn't help at all for THD+N...

Samuel
Right.
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