bandsaunter/packaging/make-browse-man.py
The Dust Council 68b05a031c Decode data signals, starting with on-off keying
Much of what a scanner finds is not speech.  Doorbells, tyre-pressure
sensors, weather stations, remote controls, paging and packet radio all
carry something a receiver can read, and until now the answer was "OOK /
ASK data burst" and a WAV file.  Now the bits come out.

The observation the whole thing is built on is that whatever the
modulation, a data signal is the same shape once it has been sliced: a
train of alternating runs whose lengths carry the information.  On-off
keying gives that directly -- the carrier is up or it is down -- and
two-level FSK gives exactly the same thing from the discriminator, one
tone or the other.  So both reduce to a run-length train and everything
after that is shared.

What the runs mean is the line code, and it is worked out from the runs
alone rather than configured, because each code makes a different
prediction about which of the two histograms is the bimodal one: PWM
(EV1527, PT2262, and nearly every 433 MHz remote), PPM, Manchester, and
plain NRZ.  Four-level FSK is recognised as such and read as symbols
rather than sliced down the middle, which produces bits that mean
nothing; where a frame sync word appears the system is named outright.

Two protocols carry their own framing and checksums and so are read in
full.  POCSAG paging: all three rates tried because nothing in the signal
says which it is, every codeword checked and single-bit errors corrected
against the BCH code, and the address, function letter and message text
reported.  AX.25 as APRS uses it: the frame check has to come out right
before a frame is reported at all, and the sender's callsign goes onto
the map with everyone else's.

The hard half is refusing what is not data.  Noise sliced at a threshold
produces runs and runs produce bits, so three things guard against it:
the runs have to quantise to the line code's own grid; most of the bursts
in a capture have to decode the same way, because one lucky window in
eight is a coincidence and that is exactly what SSB voice produced; and,
much the strongest, the packet has to repeat, because bits that come back
identical six times did not come from noise.  A reading with none of that
behind it is reported as nothing at all rather than as a bit string with
a low number beside it that somebody will read anyway.  Across 27
recordings of speech, music, static, a bare carrier, Morse and PSK it
returns nothing 27 times.

A firm decode also outranks the content check, which is statistical: a
burst of keying demodulated as FM audio is a buzz and the speech detector
likes a buzz, but a frame whose own checksum came out right is not a
statistic.  Such a capture is kept and filed as data, not as voice.

What comes out is written to a _data.txt beside the recording, shown on
the live display and in the line-per-hit output, and takes the place of
the transcript at the top of saunterbrowse -- where it is searchable, so
"which page mentioned engine 4" is a question that can be asked.
`bandsaunter analyze` decodes a file you already have.

The simulator gained two honest transmitters to test against: a
pulse-width remote that repeats a real payload, and a pager that sends
real POCSAG batches with real BCH check bits.  Random keying exercises
the classifier but leaves a decoder nothing to get right.  The POCSAG
encoder lives next to the decoder rather than in the test helpers, so a
bug shared by both cannot hide.

Fixed along the way:

- Rich reads a square bracket as markup, and a decoded page is arbitrary
  text off the air.  "[/x]" in a message ended the live display with a
  MarkupError; so did typing "[/" at saunterbrowse's search prompt.
  Everything that did not come from this program is escaped now.

- Otsu returned the first bin of a plateau.  Two populations with nothing
  between them -- silence and full carrier, which is what on-off keying
  is -- make every threshold in the gap equally good, and taking the
  first put it hard against the lower population with the hysteresis band
  outside the data entirely, so nothing sliced at all.

- Estimating the symbol clock by counting along a cumulative grid is a
  fixed point: a unit two per cent small produces two per cent more
  symbols and reproduces itself exactly.  Rounding each run on its own
  converges instead, because every run votes independently.  The grid is
  then the right way to extract the bits, where rounding runs one at a
  time drifts.

- A clipped first repeat used to truncate every other repeat to its
  length.  The consensus is taken over the commonest length now.

761 -> 869 tests.
2026-08-28 12:55:37 -07:00

345 lines
11 KiB
Python
Executable file

#!/usr/bin/env python3
"""Generate the saunterbrowse manual page.
Hand-written rather than generated from a table: unlike the scanner, the
browser's surface is a dozen keys and five flags, and describing those is
prose, not a listing. The version and date still come from the program, so
the page cannot claim to document a release that was never built.
"""
import sys
from datetime import date
from pathlib import Path
sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
import bandsaunter # noqa: E402
from bandsaunter.browse import PLAYERS, SORTS # noqa: E402
PAGE = r'''.\" Generated by packaging/make-browse-man.py -- do not edit by hand.
.TH SAUNTERBROWSE 1 "{date}" "bandsaunter {version}" "User Commands"
.SH NAME
saunterbrowse \- read and listen to what a bandsaunter scan collected
.SH SYNOPSIS
.B saunterbrowse
.RI [ DIRECTORY ]
.RB [ \-\-sort
.IR ORDER ]
.RB [ \-\-filter
.IR TEXT ]
.RB [ \-\-player
.IR CMD ]
.RB [ \-\-list ]
.RB [ \-\-callsigns ]
.RB [ \-\-kml
.RI [ FILE ]]
.RB [ \-\-no\-lookup ]
.SH DESCRIPTION
A scan leaves a directory of recordings. Beside each one is a JSON file
holding what the classifier made of it, and for speech a transcript of what
was said. Reading that by hand means opening files one at a time and guessing
which are worth playing.
.PP
.B saunterbrowse
shows them as a list you move through with the arrow keys. The transcript of
whichever recording is highlighted fills the top of the screen, because that
is the part you actually want to read; underneath it are the identification,
the bands the frequency falls in, and the list itself. Pressing Enter plays
the recording.
.PP
With no
.I DIRECTORY
it opens the one the scanner writes to, taken from your saved settings, so it
normally needs no arguments at all.
.PP
It only ever reads. Nothing in the recordings directory is renamed, moved or
deleted.
.SH KEYS
.TP
.B "Up Down k j"
Move through the recordings.
.TP
.B "PgUp PgDn"
A screenful at a time.
.TP
.B "Home End"
The first and the last.
.TP
.B Enter
Play the highlighted recording. Playing a second one stops the first: two
players talking over each other is worse than either alone.
.TP
.B Space
Stop playing. With nothing playing, it starts, like Enter.
.TP
.B t
Read the whole transcript full screen, scrolling with the arrow keys. Useful
for a long net, where the panel at the top can only show the first few lines
\[em] it says so when there is more.
.TP
.B /
Filter. What you type is matched against the frequency, the filename, the
identification and
.I everything that was said,
so "was the repeater mentioned" is a question you can ask directly. Enter
accepts, Escape clears.
.TP
.B s
Cycle the order: {sorts}.
.TP
.B r
Re-read the directory. A scan running in another window is still writing to
it, and this picks up what has arrived since.
.TP
.B o
Print the highlighted recording's path and quit, for piping into something
else.
.TP
.B "? h"
The list of keys, and which audio player was found.
.TP
.B q
Quit. With a filter in force, Escape clears the filter first.
.SH OPTIONS
.TP
.BI DIRECTORY
Where the recordings are. Defaults to the scanner's output directory, or to
.B $BANDSAUNTER_OUTPUT
when that is set.
.TP
.BI \-\-sort " ORDER"
Start in this order: {sorts}. Time is newest first; duration is longest
first.
.TP
.BI \-\-filter " TEXT"
Start with only the recordings matching this, exactly as if it had been typed
at the
.B /
prompt.
.TP
.BI \-\-player " CMD"
The command used to play a recording. The path is appended as its last
argument. By default the first of these that is installed is used:
{players}.
.TP
.B \-\-callsigns
Print every callsign heard in the directory, with the licence it belongs to
and where and when it was heard, then exit.
.TP
.BI \-\-kml " [FILE]"
Write a map of where the stations heard in this directory are licensed, and
exit. Without a filename it writes
.I callsigns.kml
in the recordings directory \[em] the same file a scan writes, so a map built
this way is continued by the next scan rather than duplicated. See
.B THE MAP
below.
.TP
.B \-\-no\-lookup
Do not contact the licence database. Callsigns are still found and still
described from their prefix; only the name and address are missing.
.TP
.B \-\-list
Print one line per recording and exit, without drawing anything. This is what
to use over a pipe, in a script, or anywhere there is no terminal.
.TP
.B \-V ", " \-\-version
Print the version and exit.
.SH SOUND
Playback is handed to whichever player is installed rather than done in the
program: the recordings are ordinary WAV files, every desktop already has
something that plays them, and a browser that cannot start is worse than one
that cannot play. If none is found, everything else still works and the
message says which packages would fix it.
.PP
Over ssh there is usually no sound server at the far end. The browser and its
transcripts work regardless; only Enter has nothing to do.
.SH DETECTED CALLSIGNS
Under the transcript, headed
.BR "DETECTED CALLSIGNS:" ,
is every callsign heard in it, with the name and location on the licence.
.PP
Finding them is not a matter of one regular expression over the text as
written. A speech recogniser is poor at callsigns \[em] they are not words,
they are said one character at a time \[em] so it breaks them wherever the
speaker paused and writes the phonetic alphabet down verbatim. "KU 0W",
"K7 RA" and "kilo uniform zero whiskey" are all one callsign each, and all
three are read back correctly.
.PP
False positives are the thing to avoid: a browser that invents callsigns is
worse than one that finds none. So a run of words is only accepted when none
of its parts is an ordinary English word \[em] "or 3. Can you open 4" fits the
shape once the punctuation is gone, and is not a callsign \[em] while a single
token said in one breath is trusted, because W1BOY is a perfectly good
callsign.
.PP
The lookup uses the FCC's own licence data, published at callook.info, which
needs no account and no key. The callsign is the only thing sent, results are
cached under
.I ~/.cache/bandsaunter/
so the same net is looked up once however many nights it is recorded, and a
lookup never delays the display: the entry says "looking up" and fills itself
in.
.PP
.B \-\-no\-lookup
contacts nothing at all. Callsigns are still found, and still described from
their own structure \[em] the prefix is allocated by the ITU and the digit is
the US licensing district, so a callsign says which country and which region
it belongs to without any database. Outside the United States that is all
there is; callook.info holds US licences only.
.PP
.B \-\-callsigns
prints every callsign in the directory, who it belongs to, and each frequency
and time it was heard on, then exits.
.PP
US amateur licence records are public by law, and include the licensee's
address. That is what is shown.
.SH THE MAP
A licence says where its holder is, so a list of callsigns is also a map. The
scanner writes one as it runs and
.B \-\-kml
builds one from recordings already on disk; both write the same file, so
either can carry on from the other.
.PP
Each station is one placemark, not one per transmission: hearing the same
repeater twenty times in an evening is one station, and twenty pins stacked
on the same rooftop would say less than one. The pin holds the callsign, the
licensee, the town, the grid square, and every frequency and time it was
heard on, so clicking it answers "when did I hear this, and where on the
dial".
.PP
The file is added to rather than replaced. A scan on Tuesday continues the
map Monday made, which over a few weeks turns into a picture of what your
aerial can actually reach.
.PP
Where the licence carries no coordinates the grid square is used instead, and
the placemark says so, because a grid square is kilometres across where a
licensed address is a street. A callsign with no licence on file at all is
still recorded, in a folder named
.IR "no location on file" ,
switched off by default: that a station was heard is worth keeping even when
nothing says where it was.
.PP
KML is the format Google Earth uses.
.BR qgis (1),
.BR marble (1)
and OsmAnd open it too, and it is XML, so a scan interrupted halfway through
leaves a file that still opens.
.SH DECODED DATA
Where a capture carried data rather than speech, what was decoded takes the
place of the transcript at the top of the screen: the kind of packet, and then
the message. A pager's text, an APRS position report, or the bits and hex of a
remote control. It is searchable with
.B /
like anything else, so "which page mentioned engine 4" is a question that can
be asked here.
.PP
The text comes from the
.I _data.txt
beside the recording, or from the sidecar where there is none.
.BR bandsaunter (1)
describes how it is decoded and what has to be true before a decode is
believed.
.SH TRANSCRIPTS
A transcript appears only where a recogniser produced one, which means the
capture was judged to be speech and
.B bandsaunter\-transcribe
was installed at the time. Where there is none, the panel says which of the
several reasons applies \[em] Morse, data, a bare carrier, or speech that was
never offered to a recogniser \[em] because those want different things done
about them.
.PP
Two places can hold the text: the JSON sidecar records what was recognised
during the scan, and the
.I _transcription.txt
beside the recording is what a later re\-run wrote. The file wins, being the
more recent of the two.
.SH FILES
.TP
.I ~/bandsaunter/
Where recordings are written, unless the saved settings say otherwise.
.TP
.IR frequency \-\- date _ time \- modulation .wav
A recording.
.TP
.IR ... .json
Its measurements and identification.
.TP
.IR ... _transcription.txt
What was said, where a recogniser heard speech.
.TP
.IR ... _data.txt
What was decoded, where the capture carried data.
.SH ENVIRONMENT
.TP
.B BANDSAUNTER_OUTPUT
The directory to open, overriding the saved settings.
.SH EXAMPLES
.PP
.RS
.EX
saunterbrowse
.EE
.RE
.PP
Open the scanner's output directory.
.PP
.RS
.EX
saunterbrowse /mnt/recordings \-\-sort frequency
.EE
.RE
.PP
Browse somewhere else, grouped by channel rather than by time.
.PP
.RS
.EX
saunterbrowse \-\-list | grep \-i "mile marker"
.EE
.RE
.PP
Search the transcripts from a script.
.PP
.RS
.EX
saunterbrowse \-\-callsigns
.EE
.RE
.PP
Everyone who identified themselves, and where they were heard.
.PP
.RS
.EX
saunterbrowse \-\-kml ~/heard.kml
.EE
.RE
.PP
The same thing as a map, to open in Google Earth.
.SH EXIT STATUS
0 on a clean exit, 1 when the directory holds no recordings, 2 when it does
not exist or there is no terminal to draw on.
.SH SEE ALSO
.BR bandsaunter (1)
.SH BUGS
The list is read when the browser opens. Press
.B r
to pick up recordings a running scan has written since.
'''
def main() -> int:
text = PAGE.format(
date=date.today().isoformat(),
version=bandsaunter.__version__,
sorts=", ".join(SORTS),
players=", ".join(name for name, _ in PLAYERS))
text = text.replace("\n\n", "\n") # troff dislikes blank lines
target = Path(sys.argv[1] if len(sys.argv) > 1
else Path(__file__).parent / "saunterbrowse.1")
target.write_text(text)
print(target)
return 0
if __name__ == "__main__":
raise SystemExit(main())