[time-nuts] Ublox neo-7M GPS
Bob Camp
kb8tq at n1k.org
Tue Aug 19 21:46:18 EDT 2014
Hi
If you have to womp up a MCU anyway, there is no reason to put in a delay chip. It’s easier / faster / more accurate to just do it all in the MCU. You have to write and maintain custom code either way.
Bob
On Aug 19, 2014, at 7:53 PM, EWKehren at aol.com wrote:
> 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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