The Signal chain page
The path from antenna to converter, drawn as a live diagram at /chain. Select a block to read what it is; select a branch or a control to change the path. This is also where inputs are enabled, disabled and inverted.
1. Reading the diagram
The diagram input buttons 1–4 choose which of the four amplifier channels is drawn. Inputs 1–3 are the H-field (magnetic) channels on the RJ45 connector; input 4 is the E-field (electric) channel on the coax connector, and its chain is simpler — its amplifiers are unity-gain followers.
| Drawn as | Meaning |
|---|---|
| Cyan outline | In the signal path right now. |
| Dim | Not selected, or not fitted on this board. |
| Dotted | Unknown — the gain chain has not been programmed yet (for example while a survey or sweep is running), so there is nothing to show. |
| Amber dashed | A change is being saved. |
The line under the diagram states the whole path in words: channel, input path, both gain stages, filter, and the total gain — including automatic when the station is steering the gain itself (gain_auto).
The selected input's own paths and filter cutoff are shown. Its filter label says measured; nominal when a confirmed filter has no valid measurement for the current path; unknown when no result is available or the check could not confirm the filter; or No working filter detected. An unconfirmed filter uses the bypass. The Filter correction row gives the correction for that input's current path; bypass means zero filter correction.
2. The blocks, left to right
| Block | What it is |
|---|---|
| Input | The antenna connection: an RJ45 pair for the H inputs, coax for the E input. The preamplifier gain of the head is declared, not measured — nothing in the hardware reports which head is on the far end of the cable. Declare it on the block: ×10 for the stock PCB 16.2 head, ×45 for PCB 23.1. An H input with no preamp declared is flagged, because without a head there is no signal at all. |
| Transformer | A 1:1 pulse transformer on the H inputs, with a nominal isolation rating of 2 kV. The E input uses a coupling network instead. |
| LC ladder | A passive filter shared by both input branches, −3 dB near 43 kHz. It shapes the signal before the first fork — and on a board without the switched-capacitor filter it is the only real low-pass in the chain. |
| First fork | On H inputs, the amplified path is ×4 with a ~1.6 kHz high-pass; the direct tap is ×1 with a ~3.3 kHz high-pass. The E input's follower path is ×1 with a ~1.5 kHz high-pass. |
| PGA A | First programmable gain stage: ×1, ×2, ×4, ×5, ×8, ×10, ×16 or ×32. |
| Second fork | Through the low-pass filter, whose cutoff the station sets (10, 15, 20, 25.2, 30, 40 or 50 kHz), or around it on the bypass. The startup self-test checks each input's filter separately. Working filters stay selected by default for noise rejection; an input with no working filter detected uses the bypass automatically. So does an input whose filter the self-test could not confirm. |
| PGA B | Second programmable gain stage, same ladder. The total gain is preamp × path × PGA A × PGA B. |
| Anti-alias, ADC | A fixed ~720 kHz section in front of the converter, then the 12-bit ADC at 500,000 samples per second. One count is about 0.79 mV at the converter; divide by the total gain to refer a reading to the antenna. |
| DAC self-test | Drawn below the chain: a signal the station injects ahead of the input branches. It enables the response sweep, gain check and delay measurement without external equipment. Detection is paused during injection, and the inputs settle before it resumes. |
3. Changing the path
Selecting a branch switches its multiplexer; the selectors on the diagram set the declared preamp gain, PGA A, PGA B and the filter cutoff. Changes apply automatically, a moment after you make them — the note under the diagram says Saved; checking hardware and then applied: the chain is now on this path. The Front end table below the diagram lists every resulting value, including the total gain calculation. While the change is being checked the note reads applied; waiting for the chain to be reprogrammed. If the save itself fails, the note reads Save failed and a Retry button appears.
These changes are configuration changes: they apply now, and the next remote configuration fetch can replace them (the default fetch interval is 5 minutes; the fleet setting is 60 seconds). If the note reads Saved, but hardware differs after 5 s, the station itself overrode the request — typically a filter that is not fitted, or automatic gain control moving the gain. What lasts and what does not: chapter 6.
4. The stage list: hardware and software
Under the diagram and the Front end table, Every stage lists the hardware and software stages in signal order. The software stages follow the digitised signal: measured Baseline and noise floor, the detection Threshold (with trigger and whether the noise floor may raise it — trig_auto), the Tone track single-frequency reject when it is in use, the trigger Rate over the last 60 seconds with any rate-cap skips, and Send: packets sent and packets held back by send_gap. Select a row of the Every stage table to read its details.
If a block explanation or stage list reads Details unavailable, that explanation is not available in the firmware currently running. The input diagram and diagnostic results can still be used.
Each value carries a small label saying how it is known:
| Label | Meaning |
|---|---|
| nominal | Documented circuit values, not read back from the hardware. |
| assumed | Derived from the build or the board revision. The firmware cannot see the part, so a wrongly fitted board reports exactly this. |
| declared | Announced by this station rather than sensed — for example the preamp gain. |
| configured | The current value of a setting. |
| measured | Read back from the hardware, or counted live. |
The filter declaration sent with each report describes its input path and cutoff; it is shown here for information. The station corrects the timestamp using the delay for the triggering input's path. The delay result identifies whether that correction uses a measurement or the nominal fallback. If the page reports No status for N s; values may be stale; retrying every 2 s, the station stopped answering — check the network, not the antenna. On the local network this appears after three failed reads in a row, or after 6 seconds without an answer. Remote access allows longer for a reply.
5. Enabling inputs, and polarity
The row of four input buttons below the diagram switches each input on or off:
- A disabled input is excluded from detection, surveys and the Live view. At least one input must stay enabled (At least one input must remain enabled), and you cannot disable the input you are currently viewing — choose another input in the viewed / diagnostic input selector on the same row first.
- The choice is stored on the board and survives restarts and remote configuration refreshes — unlike the path changes above, this one is yours, not the fleet's.
- Use fleet channels clears your local choice and follows the remote configuration's mask again.
The input polarity buttons invert individual inputs — the same control as on the Live page — and are likewise stored on the board. A note beside each group reports the save: channels saving..., channels stored locally, following fleet channels, polarity saved, or channel save failed; retry / polarity save failed; retry — press again. After a station restart the notes read station restarted; channels reloaded and station restarted; polarity reloaded.
6. What this page does not know
The diagram's circuit values are references for the board family, not verified for every board revision. Filter status and delay are tested per input; nominal or unknown labels qualify results that lack a valid measurement. The gain stages cannot be read back — the page shows what the firmware believes it sent; the preamp gain is the value someone declared. The labels in the stage list (section 4) identify how each value is known.
The measurements that close those gaps live one page over: the response sweep measures this board's actual frequency response, and the gain check measures whether the programmed gains actually follow the ladder.