[time-nuts] PLL question

Ed Palmer ed_palmer at sasktel.net
Fri Aug 7 16:52:17 UTC 2009


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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