DENKOThe GPS page
The satellite receiver's view of the sky at /gnss. Lightning locating is multilateration, so the station's clock is as important as its antenna — this page is where you check both.
1. The sky plot and the signal bars
- The sky plot looks straight up: north at the top, the horizon at the edge, the zenith at the centre. Filled markers are satellites used in the position solution; hollow markers are only in view. Bigger marker, stronger signal. Colour names the constellation.
- A banner at the bottom counts satellites that are tracked but have no known position yet — normal right after power-on, before the receiver has collected its almanac.
- The bar chart sorts every satellite by signal strength (SNR, in dB-Hz). The marked 30 dB-Hz line separates usable signals from marginal ones: a healthy station has several bars comfortably above it.
- The Satellites table lists each one with its constellation, elevation, azimuth, SNR and whether it is used in the solution.
2. The numbers that matter
| Reading | Meaning |
|---|---|
| Fix and position | The station's coordinates, once the receiver has a solution. A height needs a 3D fix — at least four satellites; until then the page says why rather than inventing an altitude. The 3D fix also gates Blitzortung registration (chapter 6). |
| DOP (PDOP/HDOP/VDOP) | Dilution of precision: how good the satellite geometry is. Lower is better; a station that sees only a corner of the sky reads high. |
| 1PPS locked | The receiver's one-pulse-per-second time signal is disciplining the station's clock. This is the lock the GPS LED reports, and the foundation of every timestamp the station sends. |
| Measured tick rate vs nominal | The station counts its own timer against the 1PPS signal and shows the difference in ppm — that is the crystal's error, measured rather than assumed. |
3. Receiver identity and constellations
Blue boards do not all carry the same receiver — u-blox and MediaTek parts are both in the field, and they share no configuration protocol. So the station asks the receiver what it is, looks the answer up in a table of known parts, and configures only what that identity calls for. A receiver that never identifies itself is left completely alone — its timing is the whole station's timing, and guessing is how a clock gets broken. The page shows the identity it found, the firmware it runs, and what it can track.
Which constellations are used is a request, not a command (gnss_sys: GPS, GLONASS, Galileo, BeiDou). The firmware clamps the request to what the part supports and to how many systems it can track at once; GPS is never dropped. Two behaviours that are easy to misread:
- A u-blox M8 asked for GLONASS and BeiDou together does not refuse — it acknowledges and enables only one. The station notices the disagreement, re-plans, and shows the combination as quietly dropped. That is a different fault from refused, and the page says which.
- Older receivers speak an NMEA version that has no sentence type for Galileo or BeiDou: the satellites are received and used, but never named. The station raises the receiver's NMEA version so they appear — a fix in the sentences, not in the sky.
4. The antenna supervisor
The receiver watches its own antenna circuit and reports ok, SHORT or OPEN, plus whether the antenna supply is on. This is the fastest way to tell “no antenna connected” from “bad view of the sky” — two very different afternoons. One caveat, which the page states when it applies: open-circuit detection is off by default (ant_ocd), and with it off “ok” only means “not shorted” — a disconnected antenna reads exactly like a healthy one.
The Front end line (AGC, noise, jamming indicator) is the receiver's own view of interference at GPS frequencies. An AGC near its maximum, or a jamming warning, means something nearby is shouting on the satellite band.
5. What this page cannot fix
Enabling a constellation does not make it acquirable. Cold acquisition needs a reasonably strong signal to decode each satellite's data, and adding a system to a weak antenna adds sentences, not satellites. If the bars sit below the 30 dB-Hz line, the answer is a better view of the sky — move the antenna — not more constellations.