[time-nuts] CW12-TIM vs M12M and the world

Ed Palmer ed_palmer at sasktel.net
Thu Mar 29 15:50:27 UTC 2012


On 3/29/2012 12:54 AM, Ulrich Bangert wrote:
> Thomas,
>
>> The sawtooth error on the Motorola M12+ is about +/- 25ns, while the
>> CW12-TIM has a sawtooth error of +/- 2 ns, so correcting for the
>> sawtooth error is not as critical with the CW12-TIM.
> The first claim
>
>> The sawtooth error on the Motorola M12+ is about +/- 25ns
> is correct but are you absolutely sure that the second claim is correct
> too?????
>
> It would mean a factor>10 improvement of the CW12-TIM against the M12 which
> is hardly believeable.

Believe it.  I've made multiple test runs where I use an HP 5372A to 
measure 1000 pulses of the CW12.  The Standard Deviation is always < 5 
ns with a max-min range of < 30 ns.  That's without any type of error 
correction - straight from the GPS receiver to the 5372A.  A clue to the 
performance is a line in the datasheet that says the clock speed is "up 
to 120 MHz".  Maybe not fast enough to justify +/- 2 ns., but in the 
ball park.

I am rather surprised that they're adding sawtooth correction.  This 
unit has been around for some years.  The Motorola firmware isn't even a 
standard offering anymore.  You have to ask for it.  It'll be 
interesting to see what they come up with considering that the datasheet 
says that the resolution on the 1 PPS signal is "< 5 ns".  There doesn't 
seem to be much room for correction there.

Ed


> Best regards
> Ulrich Bangert
>
>> -----Ursprungliche Nachricht-----
>> Von: time-nuts-bounces at febo.com
>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Tom Knox
>> Gesendet: Mittwoch, 28. Marz 2012 20:42
>> An: Time-Nuts
>> Betreff: [time-nuts] CW12-TIM vs M12M and the world
>>
>>
>>
>> I spoke with Navsync about some of the issues we are
>> discussing and this was their response. I just received mine
>> and will try to test it over the weekend. 1. Is CW12-TIM
>> compatible with Motorola M12 ?>>   The CW12 is designed to be
>> compatible with the M12 although there are
>> some differences.  The main hardware differences are listed
>> on page 7 of  the CW12 User Manual
>> (http://www.navsync.com/docs/cw12-tim_um.pdf).  2.  According
>> to the customer, M12 has a Sawtooth Correction Error&
>> Hanging Bridge Error? Does CW12 have a solution for these type of
>> errors? How these errors are taken care of in CW12?>>
>>   The Hanging Bridge Error is a pattern seen in the sawtooth
>> error that
>> occurs as the local clock frequency changes.  The standard Motorola
>> Binary software for the CW12-TIM does not have the sawtooth
>> correction
>> field in the @@Hn command implemented, but NavSync is currently
>> developing this and it will be available in future standard releases.
>>   The sawtooth error on the Motorola M12+ is about +/- 25ns, while the
>> CW12-TIM has a sawtooth error of +/- 2 ns, so correcting for the
>> sawtooth error is not as critical with the CW12-TIM.
>>
>> Thomas Knox
>>




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