[time-nuts] PLL question

Richard W. Solomon w1ksz at earthlink.net
Fri Aug 7 19:31:54 UTC 2009


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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