[time-nuts] Trimble Mini-T Timing Glitches

jimlux jimlux at earthlink.net
Thu Nov 30 20:06:09 EST 2017

On 11/30/17 3:05 PM, Leo Bodnar wrote:
> Completely off-topic comment while on the subject:
> I can't see how randomly selected 1ms of data can contain unambiguously detectable start of C/A code.
> If NAV data bit phase flip occurred within this 1ms of data then correlation search will most probably fail.
> Yes, the probability of this is only 5% (assuming equal number of 1s and 0s in NAV message) but still not zero.

I believe that Nav bits only flip at code epoch boundaries (actually, 
every 20 code epochs), it can't change in the middle of a 1023 chip 
sequence.  You use the epoch sync signal to run your symbol integrator.

> Perhaps the quote should have added "carefully chosen 1ms of data"
> At the minimum, one would typically select 2ms of sampled data when they are doing a correlation search and then they are guaranteed a full PRN sequence somewhere in there.
> Leo
>> From: Tom Van Baak Thu, 30 Nov 2017 14:43:02 -0800
>> In order to find the beginning of a C/A code in the received signal only a
>> very limited data record is needed such as 1 ms. If there is no Doppler effect
>> on the received signal, then one millisecond of data contains all the 1,023
>> chips.

Doppler does make it harder (ask the folks who did the Huygens probe)

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