[time-nuts] Ublox neo-7M GPS

[EWKehren at aol.com]

I recall when the LEA-M8F was announced that they mentioned a VCTCXO and  
maybe I wrongly assumed that they used it for sawtooth correction they also  
mention ability to control in addition an external OCXO. I previously 
suggested  using saw tooth correction information to tune a TCXO but that would 
require a  GPS module with sawtooth information and than it would be simpler 
to just use a  PIC and delay chip. Still do not understand why no one took me 
up on the offer  of chips and PCB. I guess time nuts like to talk about it 
but not fix it. How  many receivers are out there.
Bert Kehren.
 
 
In a message dated 8/19/2014 5:51:30 P.M. Eastern Daylight Time,  
kb8tq at n1k.org writes:

Hi

They are constrained by the same basic TCXO issues that  give you sawtooth 
correction. They do not use EFC to get the TCXO on  frequency. With sawtooth 
they give you a word that lets you know what’s going  on. With the NCO’s 
they often are doing very crude synthesis. They don’t put a  $48 DDS chip in 
a $10 GPS module. If you put one on a spectrum analyzer, it’s  not pretty ….

Bob

On Aug 19, 2014, at 5:46 PM, Said Jackson  <saidjack at aol.com> wrote:

> Tom,
> 
> Btw part of  my frustration with this is that we sometimes get calls from 
customers asking  why they need our or others' GPSDOs for a couple 100 
dollars when they can buy  a CW or uBlox doing "the same thing" for a fraction 
of the cost.
>  
> Most of them come back to us after evaluating these NCOs and finding  
that its not the same thing.
> 
> You get what you pay for I  guess..
> 
> Said
> 
> Sent From iPhone
>  
>> On Aug 19, 2014, at 13:01, "Tom Van Baak (lab)"  <tvb at leapsecond.com> 
wrote:
>> 
>> Hal, as long as you  maintain long-term phase lock it's a disciplined 
oscillator. So, yes, a  carrier tracking WWVB receiver with sufficiently 
stable flywheel LO is a  WWVBDO.
>> 
>> Said, too-short or too-long 100 ns cycles is  one thing. Still ok for 
many applications. But tell me more about extra or  missing pulses in the 
ublox-7. That sounds like a show stopper to  me.
>> 
>> /tvb (i5s)
>> 
>>> On Aug  19, 2014, at 2:05 PM, Hal Murray <hmurray at megapathdsl.net>  
wrote:
>>> 
>>> 
>>> SAIDJACK at aol.com  said:
>>>> its not a GPSDO though, not even a simple one  :)
>>>> It does not discipline an oscillator. It generates the  output by
>>>> mathematically calculating how many phases it  has to add/drop in a 
second,
>>>> then   digitally  adds/drops/extends/retards the phase of the output 
clock  to
>>>> achieve an average of number of desired clock  cycles.
>>> 
>>> Is there something about the term  GPSDO that says I have to do the "D" 
in the 
>>> analog domain  rather than the digital domain?
>>> 
>>> I agree that  current technology doesn't give results that are useful 
for many  
>>> applications that currently use GPSDOs.  What if the  clock ran at a 
GHz?  10 
>>> GHz?  Sure, it would have  spurs, but would it be useful for some 
applications?
>>>  
>>> Is a GPSDO still a GPSDO if the D/A driving the VCXO only has  a few 
bits?  
>>> How many bits does it need to be a real  GPSDO?
>>> 
>>> Is a battery powered wall clock  listening to WWVB at 2 AM a WWVDO?  
It's got 
>>> a pretty  good ADEV if you go out far enough.
>>> 
>>> --  
>>> These are my opinions.  I hate spam.
>>>  
>>> 
>>> 
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