Hear every sensor in the garden, not only the loudest one

Reported as reading nothing at all with several sensors in range.  Two faults,
either of which is enough on its own, and both of them things I assumed rather
than checked -- this was written against messages I generated myself and never
against a sensor.

The first is the threshold.  Bursts were found by setting one level per second
of band, halfway between the noise floor and the loudest thing in that second.
That is the obvious way to write it and it is wrong: a sensor on the windowsill
and a sensor at the end of the garden differ by forty decibels, so a level set
halfway to the near one sits above everything the far one ever does.  The far
ones do not come through weakly, they vanish -- and vanish only while the near
one is transmitting, which is as confusing a symptom as radio produces.  A
block with one loud sensor in it yielded exactly one sensor however many were
out there.

Finding bursts is now two passes.  The first asks only where anything happened
at all and asks it against the noise -- the bottom fifth of the second, which
is noise however busy the rest was, and which does not move when something
loud arrives.  Whatever clears that is grouped into regions, and the second
pass re-thresholds each region against its own high and low.  Every sensor is
sliced at its own amplitude.  Six sensors spanning eighty times in strength
now all come back from one second of band.

The second fault is that the slicer knew how a bit is drawn.  It read a pulse
by comparing it with the gap that followed, which is right when the gap is the
complement of the pulse so that every bit takes the same time, and wrong when
the gap is a fixed spacer: a two-hundred-and-twenty microsecond pulse against
a two-hundred microsecond spacer is the longer of the two and reads as a one,
which is the wrong bit, and then every message fails its checksum having said
nothing about why.  Nothing is assumed now -- not which of the pulse and the
gap carries the bit, not whether the gap is a complement or a spacer, not
which of long and short means one.  The same burst is read half a dozen ways
and the checksums say which reading it was, at most one being able to satisfy
one.  Copies are counted per message rather than per reading, or two readings
of one burst would corroborate each other and the rule protecting the two
thinly-checked models would protect nothing.

Both were caught the same way: by measuring, rather than by reading the code
again.  A thousand seconds of the invented garden still yields no sensor that
is not there, and reception of the ones that are is up by a quarter, because
bursts that used to be masked now decode.

And, because none of the above should have needed me: `bandsaunter weather
--diagnose` prints each second taken apart stage by stage -- the noise, the
level a burst must clear, the loudest thing in the block, then every burst
with the lengths of its pulses and gaps and whatever was made of them.  Those
lengths are the useful part: a real message has two or three of them and
nothing in between, which says at a glance whether the trouble is the radio or
the arithmetic.  At the end it says which of five things it was: nothing
arriving, nothing above the noise, something never keyed, bursts that framed
as nothing, or messages that framed and arrived only once.  `--save-iq FILE`
keeps the raw samples for whatever that cannot settle.

Full suite 2286 passed; the new work checked against six deliberately broken
builds.  Built as 2026-09-07_02.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016PsWPTweCT6pwxKngvVxcg

INSTALL.md

@@ -216,6 +216,13 @@ aerial: a quarter-wave whip is 17 cm, which the stock telescopic aerial does
 if it is collapsed to about that. `bandsaunter weather --simulate` runs the
 whole thing without one.
 
+If sensors you know are in range are not appearing, `bandsaunter weather
+--diagnose` prints each second of band taken apart stage by stage and says
+which of the four possible faults it is — nothing arriving, nothing above the
+noise, a burst that sliced into the wrong shape, or bits that came out and
+failed their checksums. The README section on it explains how to read the
+output.
+
 **Aircraft and callsign lookups need no installation**, only a network. They
 ask public registers about a callsign or a 24-bit address and cache the
 answers for a month; `--no-lookup` turns them off, and what the address and