New feature: SNR report screen

A project log for GPS Clock

A simple desk clock that gets extremely accurate time from GPS

Nick SayerNick Sayer 04/20/2020 at 20:130 Comments

I've added a new feature to the v5 firmware... the first screen in the menu system is now a signal quality report. The hour digits say "nX" where X is the number of satellites in view (this is reported by GPGSV). Numbers higher than 9 will be hex characters, so A, b or C. Normally this should be C (12). The minute/second digits are Sxx where xx is the highest SNR value reported in the active GPGSV sentence fragments - that is, the best SNR value reported. The 10th of a second digit will show the number of satellites that are currently being used for the fix (that is, the number of PRNs listed in the GPGSA sentence).

In general, you want an absolute bare minimum of 4 satellites contributing to the fix. With a good antenna this number should be more like 8 or 9. You'll likely always see the number of satellites in view as 12, as that's simply taken from the almanac as the 12 closest ones. SNR values above 40 are excellent. 35-40 are good, 30-35 are barely adequate, and under 30 are bad. The receiver is configured with a default SNR mask of 27, so numbers below that mean that no satellites are good enough to use.

If you have a v5 or v6 clock and a PDI capable programmer, you can update the flash yourself. If not, you can send your clock to me and I'll do it for you.