[time-nuts] Darn you people....

[Bert, VE2ZAZ]

Luis,

You said: <<Furthermore the frequency counting resolution is 16 seconds, so the ZAZ gpsdo won't lock better than 0.0625Hz.>>


On my GPSDO design, a single 16-second frequency sample does have a resolution of 0.0625Hz. But the FLL firmware does averaging over as many samples as you want before adjusting the OCXO. So I don't agree with your statement that the ZAZ gpsdo won't lock better than 0.0625Hz. In fact, I have never seen my design go worse than 1x10E-9. It usually sit below 5x10E-10. This concurs with the many reports I got from other users.


Please elaborate.

Thanks,

Bert, VE2ZAZ




Message: 3
>Date: Tue, 03 May 2011 18:14:30 +0100
>From: Luis Cupido <cupido at mail.ua.pt>
>To: Discussion of precise time and frequency measurement
>    <time-nuts at febo.com>
>Subject: Re: [time-nuts] Darn you people....
>Message-ID: <4DC037F6.5090206 at mail.ua.pt>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>Bob,
>
>You must be aware that the VE2ZAZ GPSDO does not lock the 10MHz phase to 
>the phase of the 1pps. It is a frequency counter which uses the 
>frequency error to correct the 10MHz VCXO. So it is a frequency locked 
>loop FLL.
>
>By definition on a PLL you will have the phase error being used to 
>compensate the 10MHz VCXO
>On a FLL a frequency error is required to compensate the 10MHzVCXO
>
>While having a permanent very very slow OCXO trend (drift or aging)
>a PLL(order 2) will exhibit a constant phase error while the frequency 
>is right. With an FLL it will have a constant frequency error.
>
>Furthermore the frequency counting resolution is 16 seconds, so
>the ZAZ gpsdo won't lock better than 0.0625Hz.
>A PLL scheme, thunderbolt, the old Brook Shera's, the 10KHz James 
>Miller's, or my reflock (I or II) will get you always on the ballpark.
>
>
>This PLL/FLL aspect is a subtle difference that has absolutely no 
>expression whatsoever for radio-ham applications both TX and RX on HF to 
>microwaves etc. application to which it was targeted and serve very well.
>
>
>But you will surely start to see these small aspects when you step into 
>the next level of timenutness !!!
>Apparently you have both feet there... looking at sub Hz you're infected
>that's a fact ;-)
>
>
>Luis Cupido.
>ct1dmk.
>
>