Empathy List Archives

time-nuts@lists.febo.com

Discussion of precise time and frequency measurement

Re: [time-nuts] SI532X Chips Close In Spurs (Somewhat Long)

Hal Murray

Tue, Jan 9, 2018 6:37 AM

I was hoping someone who knows these devices might have some insight into
what the issue is and how to determine which plans will not provide close in
spurs, without requiring testing. Any suggestions are appreciated.

If you look at the binary of the word that goes into a DDS adder, the ones
with more low order bits have closer in spurs. Think of that word as a
fraction, binary point on the left rather than right.

If your adder word is 0.001 (binary) it will divide by 8, no spurs.
If you have 0.00100001, it will divide by a little less than 8 and have spurs.

--
These are my opinions. I hate spam.

marklgoldberg@gmail.com said: > I was hoping someone who knows these devices might have some insight into > what the issue is and how to determine which plans will not provide close in > spurs, without requiring testing. Any suggestions are appreciated. If you look at the binary of the word that goes into a DDS adder, the ones with more low order bits have closer in spurs. Think of that word as a fraction, binary point on the left rather than right. If your adder word is 0.001 (binary) it will divide by 8, no spurs. If you have 0.00100001, it will divide by a little less than 8 and have spurs. -- These are my opinions. I hate spam.

Mark Goldberg

Tue, Jan 9, 2018 9:23 PM

On Mon, Jan 8, 2018 at 11:37 PM, Hal Murray hmurray@megapathdsl.net wrote:

If you look at the binary of the word that goes into a DDS adder, the ones
with more low order bits have closer in spurs.

Which of the setting is the binary word going into the DDS adder? I think
this uses a SI5328, and it is not described as a DDS chip in the data
sheet, but I am far from knowledgeable about this device.

I don't know what the output of the GPS is that goes into the SI5328.

Thanks,

Mark

On Mon, Jan 8, 2018 at 11:37 PM, Hal Murray <hmurray@megapathdsl.net> wrote: > If you look at the binary of the word that goes into a DDS adder, the ones > with more low order bits have closer in spurs. Which of the setting is the binary word going into the DDS adder? I think this uses a SI5328, and it is not described as a DDS chip in the data sheet, but I am far from knowledgeable about this device. I don't know what the output of the GPS is that goes into the SI5328. Thanks, Mark