FLEX-GO v1.0.0

A complete Go implementation of the Motorola FLEX pager protocol — encoder, decoder, and everything in between. CLI layout mirrors pocsag-golang.

What it can do

• Encode FLEX messages as WAV audio (1600/2, 1600/4, 3200/2, 3200/4, 6400/4)
• Decode those WAV files back to text with a native PLL demodulator
• BCH(31,21) codewords with Motorola 4-bit checksum validation
• Capcode addressing with alphanumeric, numeric, and tone page types
• Frame Information Words (FIW) and Block Information Words (BIW)
• JSON output for scripting and API integration
• Pure Go — no CGO or external demod tools required

---

Installation

# Encoder
go install github.com/sqpp/flex-golang/cmd/flex-encode@latest

# Decoder
go install github.com/sqpp/flex-golang/cmd/flex-decode@latest

Or build from source:

git clone https://github.com/sqpp/flex-golang.git
cd flex-golang
make build          # Linux/macOS
make.bat build      # Windows
# Binaries land in: bin/flex-encode, bin/flex-decode

---

Encoder (flex-encode)

Generate a FLEX message as a WAV file.

Required (unless using --reference or --messages):

• -a / --address — pager address / capcode (1..2097151)
• -m / --message — the message text

Optional:

• -o / --output — output WAV file (default: output.wav)
• -f / --function — 2 = tone, 3 = numeric, 5 = alphanumeric (default: 5)
• --mode — FLEX mode: 1600/2, 1600/4, 3200/2, 3200/4, 6400/4 (default: 1600/2)
• --cycle / --frame — FIW cycle and frame fields (optional)
• --reference — encode the known-good PDW reference page from tests/test_1600.wav
• --messages / --messages-file — JSON file with a list of message objects
• -j / --json — print result as JSON instead of human-readable text
• -v / --version — show version info

Examples:

# Basic message
flex-encode -a 1913 -m "HELLO WORLD" -o message.wav

# Long flags
flex-encode --address 1913 --message "HELLO WORLD" --output message.wav

# Reference page (cap 1913, cycle 3, frame 111)
flex-encode -o reference.wav --reference

# 3200/4 mode
flex-encode -a 1913 -m "FAST MSG" --mode 3200/4 -o fast.wav

# JSON output (great for scripts)
flex-encode -a 1913 -m "TEST" -o test.wav --json

Normal output:

✅ Generated message.wav
   Address: 1913, Function: 5, Baud: 1600, Message: HELLO WORLD
   Size: 220104 bytes, Duration: 2.50 s

Decode: flex-decode -i message.wav

JSON output:

{
  "success": true,
  "output": "message.wav",
  "address": 1913,
  "function": 5,
  "message": "HELLO WORLD",
  "baud": 1600,
  "type": "alphanumeric",
  "size": 220104,
  "duration_s": 2.495
}

---

Decoder (flex-decode)

Decode a FLEX WAV back to text.

Options:

• -i / --input — input WAV file (required)
• --no-tones — filter out tone-only messages
• -j / --json — JSON output
• -v / --version — show version info

Examples:

flex-decode -i message.wav
flex-decode -i message.wav --json
flex-decode --version

Normal output:

FLEX-1600/2: Decoded messages:
Address: 0001913  Function: 5  ALPHA    Message: HELLO WORLD

JSON output:

{
  "success": true,
  "baud": 1600,
  "messages": [
    {
      "address": 1913,
      "function": 5,
      "message": "HELLO WORLD",
      "type": "alphanumeric"
    }
  ]
}

---

Using as a Go library

Encode and write a WAV:

import flex "github.com/sqpp/flex-golang"

msg := flex.EncodeMessage{Capcode: 1913, Type: "alpha", Text: "HELLO WORLD"}
wav, _, _, err := flex.EncodeToWAVBytes([]flex.EncodeMessage{msg}, flex.Mode1600_2, 0, 0)
os.WriteFile("output.wav", wav, 0644)

Decode a WAV:

wavData, _ := os.ReadFile("message.wav")
messages, err := flex.DecodeFromAudio(wavData)
for _, msg := range messages {
    fmt.Printf("Message to %07d: %s\n", msg.Capcode, msg.Text)
}

Key functions:

Function	Description
EncodeToWAVBytes(messages, mode, cycle, frame)	Encode messages to WAV bytes
EncodeToWAVFile(messages, path, mode, cycle, frame)	Encode and write a WAV file
DecodeFromAudio(wavData)	Decode a WAV into messages
DemodulateRawFrames(wavData)	Demodulate to raw phase codewords
EncodeModeNames()	List supported encoder modes
EncodeModeBitRate(mode)	On-air bit rate for a mode name

---

Testing

go test -v ./...

Tests live in the tests/ directory. Reference captures (test_1600.wav, test_3200.wav, test_6400.wav) are included for roundtrip and decode validation.

---

About addresses

FLEX addresses are capcodes in the range 1..2097151. The encoder and decoder use the full capcode value. Function codes follow the FLEX vector type field (2 = tone, 3 = numeric, 5 = alphanumeric).

---

Credits

Part of PagerCast. Decoder logic references multimon-ng demod_flex.c and PDW Flex.cpp.

License

BSD-2-Clause — see LICENSE.