[time-nuts] An (unknown?) nasty feature of the DDS principlefortime nuts applications

[Mike Feher]

Well, do not feel bad. I am now in my 66th year and still learning. BTW, I
built my first DDS back around 1970. Hard to believe. About the same time
that I built my first digital filter. Used all discrete components and back
then we still called them recursive and non-recursive. We never heard the
term DSP till much much later. I remember using the "Remez Exchange
Algorithm" to go from the S plane to the Z plane. Of course we also used the
common "Matched Z" and others as well. My senior project in the late 60's
was a switched capacitor filter. Seems like yesterday, and now I am an old
man with 5 grandkids :). Regards - Mike

Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 office
908-902-3831 cell


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Ulrich Bangert
Sent: Tuesday, January 25, 2011 2:01 PM
To: Discussion of precise time and frequency measurement
Cc: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] An (unknown?) nasty feature of the DDS
principlefortime nuts applications

Bob,
I don't know the 33250 from my own experience but after all my Stanford
Research DS345 buy on ebay may not have been the best decision in my life.
At best I can say that I learn something new every day despite being at the
childish age of 55!

Ulrich Bangert
Ortholzer Weg 1
D-27243 Gross Ippener
Germany

Am 25.01.2011 um 18:07 schrieb "Bob Camp" <lists at rtty.us>:

> Hi
> 
> Jitter from the sawtooth phase modulation on a DDS output is indeed a very
> real thing. I have an Agilent 33250A generator sitting here on the bench
> that makes a very nice variable jitter signal source.
> 
> Bob 
> 
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Ulrich Bangert
> Sent: Tuesday, January 25, 2011 9:59 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] An (unknown?) nasty feature of the DDS
> principlefortime nuts applications
> 
> Ahhh,
> 
> I see what you mean because a few pages later there is word of a "phase
> accumulator". But this phase accumulator is a part of the electronics that
> is responsible for generating the control voltage of a VCO that enables
the
> device to produce odd frequencies despite the integer dividers in the main
> loop. That IS different from what a phase accumulator's task is in a DDS.
> 
> 73s de Ulrich, DF6JB 
> 
>> -----Ursprungliche Nachricht-----
>> Von: time-nuts-bounces at febo.com 
>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Ulrich Bangert
>> Gesendet: Dienstag, 25. Januar 2011 15:35
>> An: 'Discussion of precise time and frequency measurement'
>> Betreff: Re: [time-nuts] An (unknown?) nasty feature of the 
>> DDS principlefor time nuts applications
>> 
>> 
>> Gerhard,
>> 
>> see page 8.6ff of the service manual to see that the HP3325 
>> is not DDS based but uses a "Fractional N Synthesizer scheme" 
>> which is something completely different and is not prone to 
>> the described effects. Nevertheless it is true that the 
>> HP3325 contibutes phase noise to the measurement but I had 
>> anticipated that this was clear to everybode in the auditorium.
>> 
>> 73s de Ulrich, DF&JB
>> 
>>> -----Ursprungliche Nachricht-----
>>> Von: time-nuts-bounces at febo.com
>>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von dk4xp at arcor.de
>>> Gesendet: Dienstag, 25. Januar 2011 15:14
>>> An: time-nuts at febo.com
>>> Betreff: Re: [time-nuts] An (unknown?) nasty feature of the 
>>> DDS principle for time nuts applications
>>> 
>>> 
>>> 
>>> Don't forget that your HP3325 is DDS-based, too, so it adds
>>> its own phase error sawtooth.
>>> 
>>> 73, Gerhard dk4xp
>>> 
>>> 
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