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

[Luis Cupido]

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.





Bob Bownes wrote:
> First it was building a VE2ZAZ GPSDO with an 10881 I happened across.
> Next came the TICII's followed closely by the 5370B. Then the
> thunderbolt. Now it's time to break down and get 10Mhz/5Mhz
> distributed to all the instruments in the lab. (Still looking for a
> distribution amp)
> 
> Now the ZAZ GPSDO and the thunderbolt are side by side on the bench.
> Both said they were locked last night. But they were about 0.10hz
> apart. Now the GPSDO voltage adjust is all the way to the bottom rail.
> 
> I have no idea what time it is!
> 
> Grrr. :)
> 
> I suspect the 10881. :(
> 
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