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 <[email protected]>
Sent: Aug 7, 2009 9:52 AM
To: Discussion of precise time and frequency measurement <[email protected]>
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 <[email protected]>
Sent: Aug 7, 2009 1:32 AM
To: [email protected]
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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