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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 9th Jan 2021, 11:04 pm   #181
Radio Wrangler
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Default Re: Replacement for HP8640B signal generator

Crystal oscillators are needed as the buck-stops-here low phase noise sources for even the best synthesisers. It's not well known that Rubidium and Caesium 'atomic' frequency standards are dirty devils, short term. They have good long term stability, but you need them to slowly control a clean quartz oscillator to get both low phase noise and long term stability.

Charles Wenzel published some articles in RF Design magazine and elsewhere on low phase noise crystal oscillator design (His firm Wenzel Associates may have them on its website - they sell low noise oscillators amongst other things)

David
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Old 10th Jan 2021, 11:28 am   #182
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Default Re: Replacement for HP8640B signal generator

Thanks, David. This simple Colpitts oscillator seems to fit the bill

https://wenzel.com/wp-content/uploads/xtalosc1.pdf

In the yellow comments he says it is capable of extremely low noise when powered with a low noise regulator (or your PP3 I guess).

Sadly the fun and games being played with new VAT rules this year prevent the Australian AD9951 kit vendor selling his wares to me, at least in the short term: "at this stage we cannot sell to you as I don’t have an EORI number, but I will work on sorting this out".

Alan
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Old 12th Jan 2021, 8:48 pm   #183
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Default Re: Replacement for HP8640B signal generator

I made contact with an ex-pat (ex- KW Electronics) in New Zealand who has designed and built an AD9951 DDS PCB and even written a C library to set the output frequency. He's sending me a board in the post. What a nice chap.

Alan
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