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: [email protected]
[mailto:[email protected]] 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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