[time-nuts] Austron PRR-10 GPS discliplined Rb...

[Dr Bruce Griffiths]

Hal Murray wrote:
>> I don't understand this area well enough.  Can somebody give me a few (more) 
>> hints?
>>
>> Are we talking analog filters in hardware or software filters in a small CPU?
>>
>> How narrow an analog filter can I purchase or make?  (at reasonable price or 
>> board space or design time or whatever)
>>
>> How close do the spurs get?  I thought they got quite close if the DDS 
>> parameters were close to a good frequency.  Do they get smaller as they get 
>> closer, or something convenient like that?
>>
>> What's the term for the set of frequencies that a DDS can make with no spurs? 
>>  Say with a divide by 8.  I'm guessing that the criteria for that is 
>> something like
>> no bits left on in the low bits when the carry out of the low bits happens.  
>> By low bits I mean the ones the A/D doesn't see.
>>
>>
>>   
>>     
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Hal

Some references on DDS spur analysis

http://tycho.usno.navy.mil/ptti/ptti2005/paper8.pdf

http://www.highfrequencyelectronics.com/Archives/Oct06/HFE1006_Groulx.pdf

http://marstech.jpl.nasa.gov/tdaPublications/AnAdvSynthesizedUltra-StableOscillatorforS-CApplic.pdf

http://www.xilinx.com/bvdocs/ipcenter/data_sheet/dds_ds558.pdf

Another technique for reducing spurs whilst raising the noise floor is 
to use to dither the DDS frequency tuning word.

http://www.patentstorm.us/patents/6785345-description.html

http://www.patentstorm.us/patents/5598440-description.html
Bruce