Module: PWN::SDR::Decoder::APT

Defined in:
lib/pwn/sdr/decoder/apt.rb

Overview

Pure-Ruby NOAA APT (Automatic Picture Transmission) decoder for the 137 MHz polar-orbiting weather satellites (NOAA-15/18/19).

APT is a 2400 Hz AM subcarrier inside a ~34 kHz-wide FM downlink carrying two 909-pixel image channels at 2 lines/second (2080 words/line). This module envelope-demodulates the 2400 Hz carrier from audio, resamples to 4160 words/sec with continuous phase, and aligns the initial line on a Sync-A correlation candidate. Fixed-rate rows update a bounded rolling P5 PGM; there is no drift tracking or satellite identification. Line contrast is normalized independently. No sox, no noaa-apt.

Defined Under Namespace

Classes: Demod

Constant Summary collapse

WORDS_PER_LINE = 
2080
LINES_PER_SEC = 
2
WORD_RATE =

4160 Hz

WORDS_PER_LINE * LINES_PER_SEC
SYNC_A =

Sync-A: 7 cycles of 1040 Hz square = 1 1 0 0 repeated 7 times

(Array.new(4, 0) + ([1, 1, 0, 0] * 7) + Array.new(7, 0)).freeze

Class Method Summary collapse

Class Method Details

.authors ⇒ Object

Author(s)

0day Inc. [email protected]



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# File 'lib/pwn/sdr/decoder/apt.rb', line 173

public_class_method def self.authors
  "AUTHOR(S):\n  0day Inc. <[email protected]>\n"
end

.decode(opts = {}) ⇒ Object 



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# File 'lib/pwn/sdr/decoder/apt.rb', line 149

public_class_method def self.decode(opts = {})
  freq_obj = opts[:freq_obj]
  raise 'ERROR: :freq_obj is required' unless freq_obj.is_a?(Hash)

  want_iq = opts[:source] || opts[:file] || freq_obj[:iq_source] || freq_obj[:iq_file]
  rate = if want_iq
           opts[:sample_rate] || freq_obj[:iq_rate] || 48_000
         else
           opts[:rate] || 48_000
         end
  demod = Demod.new(rate: rate, out_path: opts[:out_path], max_lines: opts.fetch(:max_lines, 1024))
  common = opts.merge(freq_obj: freq_obj, protocol: 'NOAA-APT', demod: demod)
  if want_iq
    PWN::SDR::Decoder::Base.run_iq(common.merge(
                                     sample_rate: rate.to_i, fm_demod: true, fallback: :raise,
                                     note: 'NOAA APT: FM-demod I/Q then 2400 Hz AM envelope → rolling PGM.'
                                   ))
  else
    PWN::SDR::Decoder::Base.run_native(common.merge(rate: rate.to_i))
  end
end

.detect(opts = {}) ⇒ Object

Energy detection only; does not identify or decode APT payloads.

Supported Method Parameters

APT.detect(freq_obj: Hash, threshold: 8.0, on_frame: Proc)



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# File 'lib/pwn/sdr/decoder/apt.rb', line 141

public_class_method def self.detect(opts = {})
  Base.run_detector(opts.merge(
                      protocol: 'APT',
                      note: 'Energy detection only; no protocol payload decoding.',
                      describe: proc { |_burst| { event: 'detection', capability: 'energy-detection', decoded: false } }
                    ))
end

.help ⇒ Object

Display Usage for this Module



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# File 'lib/pwn/sdr/decoder/apt.rb', line 179

public_class_method def self.help
  puts "USAGE:
    # Detect energy only (not protocol payloads); accepts Base runner controls.
    #{self}.detect(freq_obj: {}, threshold: 8.0, on_frame: nil)
    # Run decode and return its result
    #{self}.decode(
      freq_obj: 'required - freq_obj returned from PWN::SDR::GQRX.init_freq',
      source: 'optional - source value consumed by #decode',
      file: 'optional - filesystem path',
      out_path: 'optional - out path value consumed by #decode',
      sample_rate: 'optional - I/Q audio rate Hz (default 48000 or freq_obj[:iq_rate])',
      rate: 'optional - native audio rate Hz (default 48000)',
      max_lines: 'optional - rolling image height limit (default 1024)',
      on_frame: 'optional - callback receiving each line Hash after atomic PGM update',
      output: 'optional - IO for immediate JSONL events (default stdout)',
      interactive: 'optional - stop on ENTER (default true)',
      duration: 'optional - maximum stream seconds',
      stop: 'optional - callable cancellation predicate',
      queue_size: 'optional - bounded Base input queue size',
      log_file: 'optional - JSONL log path or false to disable'
    )

    # Print the AUTHOR(S) string for this module.
    #{self}.authors
  "
  constants.sort
end