[time-nuts] Logging and correlating NMEA messages with TICC timestamp

[John Ackermann. N8UR]

Just a note about possible spurious pulses with the TICC.  The input circuit is a 3.3v logic gate that's 5v-safe.  Some PPS signals have much greater peak amplitude than that (e.g., the HP atomic clocks).

Experience has shown that these pulses don't know have enough energy to damage the input, but the voltage can cause ringing that results in occasional double pulses.  So use a scope to look at the pulse and if its peak is more than about 5v, use an attenuator to knock it down.  Also, make sure the pulse is terminated in a 50 ohm load at the TICC input.

John

On Jun 24, 2019, 2:00 AM, at 2:00 AM, "Forrest Christian (List Account)" <lists at packetflux.com> wrote:
>I have a couple of GPS receivers I'm experimenting with that I've been
>using a TICC to gather timestamps of the 1PPS output to ascertain
>their relative quality.
>
>In the process of doing this, I've discovered that some of the 1PPS
>outputs are not as stable as I'd like them to be.  For instance, the
>one currently on my bench emits stuff like this every once in a while:
>
>330364.902989667231 chA
>330365.582893064933 chA
>330365.584094826326 chA
>330365.902989679840 chA
>
>Note the 2 inserted pulses between the two correct ones.
>
>I'd like to be able to look at a log of the GPS NMEA output at the
>appropriate time for this and other events to determine if they
>correspond to some sort of GPS event.    In addition, I'd like to
>gather the phase correction data (aka quantization error) from the GPS
>(and which is spit out in a NMEA sentence as well) in a way that is
>correlated to the TICC timestamp it goes with.
>
>I know I can hack together something in python or similar to open both
>ports and log them together using a common timestamp.  But this also
>seems like something which is probably being done regularly in time
>labs around the globe so there's likely some tool to do this that I'm
>unaware of.
>
>So I guess I'm asking what everyone else is using to gather both
>timestamp data and NMEA data in a correlated way....
>
>Thanks for any input.
>
>-- 
>- Forrest
>
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