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Old 17th April 2013, 05:12 PM   #2331
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Scott,

How much of the base spread is from jitter vs noise?

ES
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Old 17th April 2013, 05:12 PM   #2332
RNMarsh is offline RNMarsh  United States
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How high was the Q ? Can you put a number on it?

To what extent would other means to get high Q result in similar increases in AM?

How can you tell it isnt from noise/jitter at/near the Fo?


-RNM

Last edited by RNMarsh; 17th April 2013 at 05:18 PM.
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Old 17th April 2013, 06:46 PM   #2333
davada is offline davada  Canada
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Quote:
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That would be a good test of a selective amplifier.
What's the difference between a selective amplifier and a high Q bandpass filter?
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Old 17th April 2013, 06:48 PM   #2334
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
How high was the Q ? Can you put a number on it?

To what extent would other means to get high Q result in similar increases in AM?

How can you tell it isnt from noise/jitter at/near the Fo?


-RNM
There is such a circuit as a Q multiplier used with lower Q bandpass filters to increase the Q. But it one more amplifier.
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Old 17th April 2013, 07:05 PM   #2335
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by RNMarsh View Post
How high was the Q ? Can you put a number on it?

To what extent would other means to get high Q result in similar increases in AM?

How can you tell it isnt from noise/jitter at/near the Fo?


-RNM
The short version? Do all high Q BP filters do this...? create AM distortion.

If the answere is No... then what caused it in your method/circuit?


PS---> I will have an AP-7722A here next week to look at. Its osc spec is less than .0002%.
I'll comapre the schematic of the VP-7723A (.0005%) to it to see how or what they did to get thd reduced.


-RNM

Last edited by RNMarsh; 17th April 2013 at 07:15 PM.
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Old 17th April 2013, 07:32 PM   #2336
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Dick,

All high Q filters create amplitude variation if the input frequency wiggles around.

The Q as defined by the 3 db bandwidth in hertz divided by the center frequency is very high but not really shown in his plot.

The example he showed is .00065% distortion. (By eyeball) If he used a clean stable oscillator he would easily be an order of magnitude better.

ES
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Old 18th April 2013, 12:39 AM   #2337
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Had some ground loop problems tonight but I just got an EMU 0204 and it seems to work fine doing simultaneous input and output. I set up tonight initially with two computers and two USB sound cards (a grounding mess). The short of it is that everything looks fine, with a sound card generated sine wave it is very stable and the THD looks to be amplifier limited. I let it run for 5 hours and the amplitude was very stable.
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Old 18th April 2013, 02:58 AM   #2338
1audio is offline 1audio  United States
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To properly determine if the close in noise is am or fm you need to compare the upper and lower sidebands. If they are in phase its amplitude, out of phase is frequency. And I don't have a clue as to how you would actually measure this, especially for random noise.

You could measure Allen deviation to test for frequency stability but that is long term stuff and probably not audible in any sense. Injection locking would make a big improvement but do nothing useful for actual distortion and possibly will make the noise higher. The output will have noise contributions from both sources.
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Old 18th April 2013, 02:59 AM   #2339
RNMarsh is offline RNMarsh  United States
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It's a very interesting means to generate a freq. Can you get lower thd from it? .00065% is very good, of course. But not better than stock K-H or Panansonic or tweaked HP 339A etc. But nice concept which i really appreciate learning about its working. How low distortion can you get out of it? More than -120? More than -130? It needs to be at least -130 to be reasonably competitive. Can it be better than Victor's?

-RNM

Last edited by RNMarsh; 18th April 2013 at 03:05 AM.
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Old 18th April 2013, 05:29 AM   #2340
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Quote:
Originally Posted by scott wurcer View Post
Had some ground loop problems tonight but I just got an EMU 0204 and it seems to work fine doing simultaneous input and output. I set up tonight initially with two computers and two USB sound cards (a grounding mess). The short of it is that everything looks fine, with a sound card generated sine wave it is very stable and the THD looks to be amplifier limited. I let it run for 5 hours and the amplitude was very stable.
If you are not already below your noise floor, then you can add an RC filter on the output and raise the noise and get 6 db less 2nd.

Of course you can parallel Wein filters, but I suspect with the quality of parts available you are at or below measurable distortion.

Scott I think using the sound card as the source is a nice improvement. Now all you have to do is make it a tracking filter. Instead of trying to build a leveler a tracker can have the knowledge of the target frequency. So using D/As for both the R and C would allow that. Relay switch R 2R or C 2C networks with good layout are the best method of doing that as far as I know.

So it should be possible to build a worlds best oscillator for fixed frequencies at modest cost.

So now you can claim -200 db as there is no way to measure it!

Keep on truckin'

ES

Last edited by simon7000; 18th April 2013 at 05:45 AM.
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