[time-nuts] PLL question

Ed Palmer ed_palmer at sasktel.net
Fri Aug 7 20:37:22 UTC 2009


Yes, you're right.  I wasn't suggesting that you were wrong.  But the 
NCO term is more common.  And I realize that you can get into a huge 
semantic argument about whether NCO and synthesizer are synonymous terms.

I get the impression that they realize that calling it a synthesizer 
might raise performance expectations higher than they are willing to 
meet.  Their support for the feature is limited at best.  After all, 
they don't even allow you to change the frequency if you have the 
Motorola software load.

Ed

Richard W. Solomon wrote:
> Gleaned from the NavSync site:
>
> "... The CW12-TIM has an on-board
> programmable NCO oscillator that
> outputs a synthesized frequency up to
> 10 MHz that is steered by the GPS
> receiver. ..."
>
> "...A Rose by any other name ..."
>
> 73, Dick, W1KSZ
>
> -----Original Message-----
>   
>> From: Ed Palmer <ed_palmer at sasktel.net>
>> Sent: Aug 7, 2009 9:52 AM
>> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>> Subject: Re: [time-nuts] PLL question
>>
>> Navsync doesn't really call it a synthesizer, they call it a Numerically 
>> Controlled Oscillator (NCO).  My tests suggest that they're doing what 
>> others have done on the 1 PPS output - change the state of the 10 MHz 
>> output (high to low or vice versa) on a transition of their internal 120 
>> MHz clock.  This means that you occasionally get a pulse that's ~8 ns 
>> shorter or (presumably) longer than normal.  My unit puts out a short 
>> pulse about 200 times per second.  Navsync has an app note where they 
>> say that for some applications a phase-locked cleanup oscillator will be 
>> required.
>>
>> Ed
>>
>> Richard W. Solomon wrote:
>>     
>>> Dumb question time:
>>>
>>> If the NavSync has an on-board synthesizer locked to GPS, why do
>>> you need to lock that to another oscillator ??
>>>
>>> 73, Dick, W1KSZ
>>>
>>> -----Original Message-----
>>>   
>>>       
>>>> From: gonzo moto <cadbloke at hotmail.com>
>>>> Sent: Aug 7, 2009 1:32 AM
>>>> To: time-nuts at febo.com
>>>> Subject: [time-nuts] PLL question
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Hi Guys,
>>>> I'm in the process of building a GPSDO which started out life based on G3RUH's design, but suffered a bit of feature creep.
>>>>
>>>> The GPS I'm using is the NavSync CW12, so I'll run the Freq_Out at 10MHz.
>>>> I'm wondering if I should run the PLL at 10MHz or if there is an advantage dividing the two signals down to (say)10KHz.
>>>> Does the averaging at 10kHz  (and introduced errors of the dividers) outweigh the 'no averaging' and no additional errors syncing at the fundamental freq?
>>>> I can think of arguments each way, but lack the test equipment to prove either way.
>>>>
>>>> Suggestions would be appreciated.
>>>>
>>>> Regards,
>>>> ian
>>>>
>>>> _________________________________________________________________
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