[time-nuts] anyone tried the cheap Lea-6T modules seen on eBay?
michael.cook at sfr.fr
Tue Nov 25 11:15:36 EST 2014
You may have seen them as in
There are other sellers with the same.
My idea was to see if one was suitable as a 1PPS locking source for my PRS10. The interest for me being that it powers directly from a USB connection and can be configured with the Ublox’s u-center software, so implementation is a no brainer.
All I needed to do was to replace the patch antenna with an SMA-F connector and add a wire for the 1PPS. Despite having less than ideal antenna position, once the survey was complete I was getting +/-20ns jitter on the 1PPS which is within spec and stable over the day.
However I was most disappointed to see that the 1PPS output voltage is only 2.16 +/-0.4V. According to spec it should be Vcc+/-0.4V and I have Vcc measuring 3.3V. I can’t see the board trace but the measured voltage is the same on the PPS pad next to the JST-SH connector and on the GPS modules pin 28 so it is not a board issue. Unfortunately this is too low to tickle the PRS10 1PPS input. I guess I could add a buffer or AND gate to fix it, but that sort of defeats the object and introduces extra jitter and offset.
It is however enough for a Raspberry-Pi GPIO input, so I have relegated it to NTP PPS.
Has anyone out there got one of these and seen the same symptoms? Or maybe you have one and it is OK? I’d like to know.
You will be able to see from the eBay photos that this a 6T-0-000 version which is an early version and it could be that they are cheap as some/all have this defect. So beware.
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