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A project log for GPS Clock

A simple desk clock that gets extremely accurate time from GPS

nick-sayerNick Sayer 07/22/2017 at 14:170 Comments

The v5 prototypes have shown some reduced sensitivity on the antenna input. The symptom has been S/N numbers in the GPGSA sentences about 10 dB lower than other units show.

Turns out that the problem is caused by a lack of bypassing on the AP2331. I'm going to add footprints for bypass caps on all future boards, but it appears that just tacking an 0805 or 0603 0.1 µF ceramic cap across the output of the 2331 is a sufficient workaround. Another option is to add an external bias-T if your antenna needs power and open the voltage selection jumper or remove the 0.033 µH bias inductor.

You can test your own clock by taping the GPS receiver serial output. Use a jumper wire to temporarily tie !RESET to ground on the programming header and watch the S/N numbers compared to the numbers while the controller is running. If there's no difference, then you don't have the symptoms. 

So far, only the versions with the XMega have shown any issues, and those aren't going to ship before the current inventory is exhausted. 

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