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HM

Hal Murray

Wed, Dec 13, 2023 9:47 AM

Jim Lux said:

This may or may not work, depending on your phase noise requirements. There
are techniques for DDSes to make the close in phase noise small (at the
expense of raising it farther out - it's always like squishing a balloon).

Could you say more about hat area? Is there a good paper or chapter of a book?

Is there a simple formula for the size and offset of the closest spurs? Do
they ever get lost in the phase noise of the main peak?

--
These are my opinions. I hate spam.

Jim Lux said: > This may or may not work, depending on your phase noise requirements. There > are techniques for DDSes to make the close in phase noise small (at the > expense of raising it farther out - it's always like squishing a balloon). Could you say more about hat area? Is there a good paper or chapter of a book? Is there a simple formula for the size and offset of the closest spurs? Do they ever get lost in the phase noise of the main peak? -- These are my opinions. I hate spam.

BK

Bob kb8tq

Fri, Dec 15, 2023 1:46 PM

Hi

On Dec 13, 2023, at 4:47 AM, Hal Murray via time-nuts time-nuts@lists.febo.com wrote:

Jim Lux said:

This may or may not work, depending on your phase noise requirements. There
are techniques for DDSes to make the close in phase noise small (at the
expense of raising it farther out - it's always like squishing a balloon).

Could you say more about hat area? Is there a good paper or chapter of a book?

You modulate the carrier to push the spurs / noise further away from the carrier. To get it working you could be pushing tuning info into the DDS at a “many MHz” sort of rate. That’s going to give you other spurs to worry about.

Is there a simple formula for the size and offset of the closest spurs?

There are formulas, to use them you would have to know a lot about the exact defects in the ADC on the example of the chip you have ( = the fine detail of the spurs will vary board to board). The spurs also will vary depending on the tuning setting. This is part of why the “modulation” approach impacts them.

Do
they ever get lost in the phase noise of the main peak?

Not if you look closely. The tricks might get you 10 db … maybe ….

Bob

--
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Hi > On Dec 13, 2023, at 4:47 AM, Hal Murray via time-nuts <time-nuts@lists.febo.com> wrote: > > > Jim Lux said: >> This may or may not work, depending on your phase noise requirements. There >> are techniques for DDSes to make the close in phase noise small (at the >> expense of raising it farther out - it's always like squishing a balloon). > > Could you say more about hat area? Is there a good paper or chapter of a book? You modulate the carrier to push the spurs / noise further away from the carrier. To get it working you could be pushing tuning info into the DDS at a “many MHz” sort of rate. That’s going to give you other spurs to worry about. > > Is there a simple formula for the size and offset of the closest spurs? There are formulas, to use them you would have to know a lot about the exact defects in the ADC on the example of the chip you have ( = the fine detail of the spurs will vary board to board). The spurs also will vary depending on the tuning setting. This is part of why the “modulation” approach impacts them. > Do > they ever get lost in the phase noise of the main peak? Not if you look closely. The tricks might get you 10 db … maybe …. Bob > > > -- > These are my opinions. I hate spam. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

JL

Jim Lux

Fri, Dec 15, 2023 5:29 PM

There are some Analog Devices datasheets and ap notes that talk about it. There’s a book by Vankka
https://link.springer.com/book/10.1007/978-1-4757-3395-2
Look at some of the second generation DDSs. (I.e. the ones that came out after the AD985x series, which are straight DDS with phase accumulator - sin/cos- dac)

And a few papers, I’ll look for them. - As for a generalized way to predict the spurs - I don’t think so, I think you have to model it for your case. We talked about it on this list about 5-10 years ago. We were looking into it to improve turnaround performance for deep space transponders, where you care a lot about close in phase noise because it affects performance for ranging. Not so much for low (~10 bps) data rates, since those are a subcarrier 10-20 kHz away.

Essentially, one technique is to predict the spur (e.g. from a table, or suitable arithmetic) and have another DDS that coherently subtracts it. Another is to put some sort of (digital) filtering in the path between the phase accumulator and the sin/cos lookup, or between the sin/cos lookup and the DAC.

On Wed, 13 Dec 2023 01:47:50 -0800, Hal Murray via time-nuts time-nuts@lists.febo.com wrote:

Jim Lux said:

This may or may not work, depending on your phase noise requirements. There
are techniques for DDSes to make the close in phase noise small (at the
expense of raising it farther out - it's always like squishing a balloon).

Could you say more about hat area? Is there a good paper or chapter of a book?

Is there a simple formula for the size and offset of the closest spurs? Do
they ever get lost in the phase noise of the main peak?

--
These are my opinions. I hate spam.

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

There are some Analog Devices datasheets and ap notes that talk about it. There’s a book by Vankka https://link.springer.com/book/10.1007/978-1-4757-3395-2 Look at some of the second generation DDSs. (I.e. the ones that came out after the AD985x series, which are straight DDS with phase accumulator - sin/cos- dac) And a few papers, I’ll look for them. - As for a generalized way to predict the spurs - I don’t think so, I think you have to model it for your case. We talked about it on this list about 5-10 years ago. We were looking into it to improve turnaround performance for deep space transponders, where you care a lot about close in phase noise because it affects performance for ranging. Not so much for low (~10 bps) data rates, since those are a subcarrier 10-20 kHz away. Essentially, one technique is to predict the spur (e.g. from a table, or suitable arithmetic) and have another DDS that coherently subtracts it. Another is to put some sort of (digital) filtering in the path between the phase accumulator and the sin/cos lookup, or between the sin/cos lookup and the DAC. On Wed, 13 Dec 2023 01:47:50 -0800, Hal Murray via time-nuts <time-nuts@lists.febo.com> wrote: Jim Lux said: > This may or may not work, depending on your phase noise requirements. There > are techniques for DDSes to make the close in phase noise small (at the > expense of raising it farther out - it's always like squishing a balloon). Could you say more about hat area? Is there a good paper or chapter of a book? Is there a simple formula for the size and offset of the closest spurs? Do they ever get lost in the phase noise of the main peak? -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

JL

Jim Lux

Fri, Dec 15, 2023 5:49 PM

https://febo.com/pipermail/time-nuts_lists.febo.com/2011-January/036289.html
https://febo.com/pipermail/time-nuts_lists.febo.com/2011-January/036351.html

might get you started.

On Wed, 13 Dec 2023 01:47:50 -0800, Hal Murray via time-nuts time-nuts@lists.febo.com wrote:

Jim Lux said:

This may or may not work, depending on your phase noise requirements. There
are techniques for DDSes to make the close in phase noise small (at the
expense of raising it farther out - it's always like squishing a balloon).

Could you say more about hat area? Is there a good paper or chapter of a book?

Is there a simple formula for the size and offset of the closest spurs? Do
they ever get lost in the phase noise of the main peak?

--
These are my opinions. I hate spam.

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

https://febo.com/pipermail/time-nuts_lists.febo.com/2011-January/036289.html https://febo.com/pipermail/time-nuts_lists.febo.com/2011-January/036351.html might get you started. On Wed, 13 Dec 2023 01:47:50 -0800, Hal Murray via time-nuts <time-nuts@lists.febo.com> wrote: Jim Lux said: > This may or may not work, depending on your phase noise requirements. There > are techniques for DDSes to make the close in phase noise small (at the > expense of raising it farther out - it's always like squishing a balloon). Could you say more about hat area? Is there a good paper or chapter of a book? Is there a simple formula for the size and offset of the closest spurs? Do they ever get lost in the phase noise of the main peak? -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

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Re: pulling some crystals