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the Precision Clock gps fix issue
Andreas Posted: 31 Jul 2020, 10:07 AM
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Hello so when I received the clock and put it together I left it outside and it got a GPS fix in under 10 minutes and that was perfect. As soon as I moved it inside however it lost the GPS fix.

And so I attempted to get it working moving from outside to inside the house until one night I had decided to leave it outside for the night and as I was walking downstairs it somehow got a GPS fix inside the house and that was excellent (sidenote: I had it attached to a power bank that's why it got a fix while I was moving it). I left it right there in the house where it got the fix for the night. In the morning I started slowly moving it to it's designated spot on my wall it took me 5 hours in total to slowly move it without it losing the fix.

Everything was good it had the fix on the wall until 6 days later when it lost the fix and didn't regain and when I moved it slightly (like 10cm away from the current place) it got the GPS fix back. And it has been like that for the entire time now. On the wall it has the fix for like couple hours then it loses it and when I slightly move it away it will gain it back again. Funny thing was that at first, I wanted to put it next to my window because I expected it to work there better but instead it worked even worse next to the window and it worked better the further it was from it.

Is there a way I could still have it on the wall and not have it lose the GPS fix?

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mit Posted: 31 Jul 2020, 11:07 AM
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yeah whatever

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That does sound annoying. One of the things to remember, and why it's so hard to be scientific about this, is that the weather affects the signal. If there's only faint reception inside the house, then a cloudy day can cause it to lose its fix.

I recently added an update to the optional steps, where I made a cable that lets you switch between power supplies without resetting the clock. It means you can power it from a battery pack outside, then bring it indoors and transfer it to a mains USB supply.

Have you tried the active antenna? It helps a bit, although it's not guaranteed to fix the problem. The best solution is to put the GPS module and antenna somewhere good, and run a cable between the clock and the module.

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Andreas Posted: 3 Aug 2020, 03:08 PM
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I've noticed that when a cloudy storm came it still had a strong GPS fix it just happens to sometimes lose it thankfully it isn't often more like in over a period of 6 or more days. About making the GPS longer, would I have to resolder it to make it longer?

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mit Posted: 4 Aug 2020, 07:08 AM
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yeah whatever

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Yes, desoldering the module is best, which can be quite difficult. A heat gun is the best option, trying to use a soldering iron is not going to work. Another option is extending the antenna only, which will require the correct impedance cable and connectors. I find the first option easier, as the UART data from the module is a lot more resilient (any old cable should work), but people have reported success with both methods.

If you use a CAT5 cable to extend it, I recommend using one of the twisted pairs for PPS + ground, and make all of the unused wires in the cable grounded too.


I just remembered that I bought an external antenna a while back, a "magnetic puck" type with an SMA connector. It needs an SMA to u.fl adapter to be used with the GPS module, but I just tried it out and it works fine, so perhaps that is the easiest option.

Last edit by mit at 4 Aug 2020, 07:08 AM

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Andreas Posted: 7 Aug 2020, 11:08 AM
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Thank you a lot for the advice I'll keep it in mind. I won't start doing anything right now since it seems to have a pretty stable GPS fix and seems to gain it back itself if it does lose it. Still thanks for the advice!

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mit Posted: 9 Aug 2020, 12:08 PM
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yeah whatever

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I added another bit to the optional instructions page about this antenna. It's labelled Trimble 66800-52, I bought it from eBay about two years ago for less than £10. There are vague references to it having a gain of 28dB. It needs a U.FL to SMA adapter to work with the clock but those are very cheap.

Thoroughly recommended - gives you a 5m cable and the antenna itself is waterproof so it can go outside. Seems to give a very stable GPS fix for me.

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