Reported as "the Doppler moves the frequency enormously", and it did: a 2 m
downlink was being shifted two megahertz across a pass instead of three
kilohertz, in the wrong direction.
The propagator library reports a range rate that is not one. Measured against
the range it is meant to be the derivative of, on this station's own cached
elements:
PO-101 library -1457.3 km/s measured +6.227 km/s
ISS library +2036.8 km/s measured -5.522 km/s
Wrong by a factor of some 250 and of the wrong sign, so the correction both
overshot and pushed the operator away from the station they could hear. Nothing
else was affected — the elevation and the passes come from the look angle, which
is right — which is why this survived: the satellite was in the correct place on
the map while the radio was told to go megahertz away from it.
So OpsLog computes it itself, as the difference between two ranges a second
apart. That cannot be wrong in either magnitude or sign: it differentiates the
very number the panel displays. Two extra propagations per call, which is
microseconds.
Two tests pin it, and both fail against the old behaviour: a range rate faster
than orbital velocity is a units mistake, and the Doppler on the two bands
satellites are worked on has a textbook size — about ±3.5 kHz on 2 m, ±10 kHz on
70 cm.
cmd/satdiag is the throwaway that found it, kept because the next report of this
shape ("the frequency moves oddly", "that pass is not real") is answered by the
same three numbers: which elements the satellite resolved to, the range rate
reported against the range rate measured, and the Doppler each transponder gets.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
25 satellites, typed by hand and never revisited. Eight of them were the
first-generation Tevel constellation, which re-entered in 2024; four more had
come down too; and the nine Tevel-2 satellites that replaced them, the Chinese
space station, AO-27, AO-123 and twenty others were simply absent. So: 44
satellites now, and a generator instead of a memory.
cmd/satgen joins three public sources on the NORAD catalog number — Celestrak's
amateur group and PE0SAT's mirror for which birds OpsLog can actually get
elements for, and SatNOGS DB for the transmitters. It is a one-shot tool, run by
hand, the same arrangement as cmd/cntygen, and it is deliberately conservative:
- It never destroys a curated entry. The hand-written plans hold things
SatNOGS does not reliably carry — a CTCSS tone, the QO-100 passband as
operators describe it — so an existing bird keeps its data and only gains
its catalog number.
- It prunes on the re-entry date, which is a fact SatNOGS publishes rather
than a judgement about which of the missing satellites are missing for good.
- It refuses a digital uplink that does not say what it is. A GMSK uplink is a
command channel far more often than a digipeater, and shipping the wrong one
invites somebody to transmit on a control frequency. An analog uplink with
both ends is a contact by construction, which is what catches the repeaters
that describe themselves only as "Mode V/U FM".
- Its output is deterministic. One satellite can hold two catalog entries —
GreenCube is 53106 in one feed and 53109 in the other — and iterating a map
picked a different one each run.
A bird now carries its NORAD number, and that is how its elements are found.
Names were the only join before, and they are written differently by every party
involved: "TIANYAN 01" and "TO-108" are one satellite that had never once met,
so TO-108 tracked nothing at all.
And the plan now reaches a station that has already run OpsLog. The editable
copy was written on the first launch and was the operator's list for ever after,
so a release adding nine satellites reached nobody who had opened the tab. It is
merged on each load instead: a satellite they already have is untouched, edits
and corrections included, and only the ones they have never seen are added.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
The foundation of the satellite branch, and nothing above it yet: where a
satellite is (SGP4 from akhenakh/sgp4, Apache-2.0 and pure Go, so the
no-cgo rule holds), where it will be (passes with an elevation floor,
because a three-degree scrape is a line in a table that will never be a
QSO), and what its motion does to a frequency.
The Doppler pair is the part worth being careful about: the two
corrections go in OPPOSITE directions. The downlink arrives shifted and
we tune to meet it; the uplink must LEAVE shifted the other way to land
on the transponder's nominal input. A test pins the signs and the size —
7 km/s on 2 m is about 3.4 kHz.
Elements keep their raw lines beside the parsed form: that is what the
cache stores and what an operator pastes by hand for a bird no feed
carries yet, which is exactly when everyone wants to hear it.
rouggyandClaude Opus 5