The region was in the menu, in the receiver group, between the sample rate and
the invented channel. That is the wrong place for it. It is the setting that
decides whether anything is heard at all, and being on the wrong one sounds
exactly like having no aerial, so it does not belong a level down among the
things that make a working receiver work slightly better.
It is now on the front page of the APRS menu, named as well as numbered, and
so is the Listen line: "north-america 144.39 MHz" rather than "144.39 MHz",
because the number alone does not say whether it is the right one and the name
alone does not say what will be tuned. A channel that is no region's says so
rather than claiming one.
The region and the frequency are separate settings -- somebody may want a
local packet network on neither -- which means they can be made to disagree.
Every place that chooses a region now goes through one function, so they
cannot.
And there is a search. `bandsaunter aprs --find-channel`, or f in the menu,
listens on each region's channel in turn and prints what was on each, then
offers to use the busiest. This answers the one question about APRS that
cannot be answered on any single frequency, because the answer *is* a
frequency: somebody who has just plugged a dongle in cannot tell a wrong
channel from a dead aerial, and that is worth a minute of listening rather
than an evening of doubt.
What it does not do is claim more than it found. A quiet channel is not proof
of an empty one -- a fixed station beacons every half hour -- so what it finds
is traffic, and when every channel comes back silent it says that this is not
the same as an empty band and points at the aerial instead.
The invented channel now honours tuning, and only carries its stations on its
own frequency. Without that the search would pass on a simulated band having
never searched anything, which is the kind of test that is worse than none.
Sixteen new tests against six deliberately broken builds. The three that
searched a whole simulated band were doing the same expensive thing three
times over and now build their results directly, leaving one real end-to-end
search; that file went from nine and a half minutes to two. Full suite 2612
passed. Built as 2026-09-20_03.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016PsWPTweCT6pwxKngvVxcg
A third section, alongside the aircraft and the weather sensors, and for the
same reason as both: a scan stops on a signal, records it and moves on, while
APRS is a two-second transmission every few minutes from a hundred stations
sharing one frequency. A sweep catches whichever happened to key up as it
passed. `bandsaunter aprs` parks on the channel and catches all of them;
`bandsaunter packets` reads a log back.
Four layers, three of them new.
The link layer was already here, opportunistically, in the generic decoder --
a correlator, NRZI, HDLC and a checksum, run on whatever a scan happened to
record. It is now a receiver. What had to change is the state that survives
a block boundary: the tail of the audio so the correlators see no edge, the
phase of the sampling loop so a bit is not lost where one block meets the
next, the tone the line was last at, and the bits themselves. A packet is
most of a second and a block is about one, so frames straddling the boundary
are not an edge case, they are most of them.
Above that, the APRS information field, which is not one format but about
twenty, chosen by the first character and accreted over thirty years.
Positions uncompressed and compressed; Mic-E, which every Kenwood and Yaesu
mobile sends and which hides the latitude inside the destination callsign
because in 1995 those six bytes were carrying the word "APRS" and nothing
else; weather with a position and without; messages, acknowledgements,
rejections and bulletins; objects and items; status; telemetry; third-party
traffic, credited to whoever originally sent it rather than to the gateway.
Course and speed, altitude, power and antenna height, range and the precision
extension, all of which ride in the comment. Every one has a writer beside
its reader, so a packet goes in and the same packet comes out.
Above that the section: a registry of who is out there and what each last
said of each kind, distances and bearings from --at, a log keeping the whole
frame under whatever was made of it, a spreadsheet, a map, and a channel full
of stations that are not there for --simulate.
One rule is worth naming because it is the difference between a decoder and a
liar. A packet whose format does not match what its first character promised
comes back as unparsed with its text intact. Thirteen characters of a
*malformed* uncompressed position are perfectly good base-91, so trying one
format and falling back to the other does not fail on a bad packet -- it
succeeds, as a confident and completely different place, usually a thousand
miles away. The specification makes the two unambiguous, a leading digit
always meaning uncompressed, and the rule is read rather than guessed at.
Two faults found by building it, both by measurement rather than by reading
the code again. The framer handed back frames it had already reported,
because it trimmed its buffer to before them rather than after -- every packet
counted twice, for ever, which only shows up once the same signal is read
across more than one block. And the invented channel truncated a
transmission at the end of the block it began in rather than carrying the
remainder over, which was invisible for as long as the simulated clock
advanced in exact seconds and put every transmission at a block boundary; the
moment it was paced against a real clock, nothing decoded at all.
204 new tests against seven deliberately broken builds, one of which survived
until a test was written for the case it actually breaks. Full suite 2597
passed. Built as 2026-09-20_02.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016PsWPTweCT6pwxKngvVxcg
The Dust Council