Mode Options
Transmit mode: read data from stdin and output FSK audio
Receive mode: decode FSK audio input to data (default mode)
Encoding Options
Use ASCII 8-N-1 encoding (8 data bits, no parity, 1 stop bit)Default for most baud rates.
Use 7-bit encoding (7-N-1)For 7-bit ASCII or protocols requiring 7 data bits.
Use Baudot 5-N-1 encoding (5 data bits)Uses Baudot/ITA-2 character encoding with LTRS/FIGS shifts.
Select Baudot USOS (US) or ITA-2 (0) character setControls which Baudot character table is used:
0: ITA-2 international standard (default)1: USOS United States standard
Output raw binary data without character decodingUseful for protocols with binary data or custom encodings.
Raw binary mode with specified number of bits per frameDisables start/stop bits and character decoding. Outputs raw bit values.
Frequency Options
Set mark (1 bit) frequency in HzOverride automatic frequency selection.
Set space (0 bit) frequency in HzOverride automatic frequency selection.
Invert mark and space frequencies (swap)Useful for inverted signal polarity or non-standard equipment.
Frame Format Options
Number of start bits per frame (0-20)Standard serial has 1 start bit. Some protocols use 0 or multiple start bits.
Number of stop bits per frame (fractional allowed)Standard values:
1.0: One stop bit (most common)1.5: RTTY standard2.0: TDD/TTY standard0.0: No stop bits (e.g., SAME protocol)
Invert start and stop bit polaritySwaps the expected mark/space values for framing bits:
- Normal: start=space(0), stop=mark(1)
- Inverted: start=mark(1), stop=space(0)
Transmit/expect most significant bit firstDefault is LSB-first (least significant bit transmitted first).
Use synchronization byte preambleFor protocols requiring sync bytes (like NOAA SAME):
- In TX: sends 16 sync bytes before data
- In RX: looks for sync byte pattern and suppresses them in output
Receive Options
Automatically detect carrier frequencyScans audio spectrum to find the carrier instead of using fixed frequencies.
Useful when frequency is unknown or may vary.
Minimum confidence threshold for signal detectionControls signal-to-noise squelch:
- Lower values: accept weaker signals, more false detections
- Higher values: require cleaner signals, fewer errors
- Typical range: 1.0 to 3.0
Maximum confidence search limitPerformance vs. quality tradeoff:
- Lower values: faster, may miss optimal frame position
- Higher values: slower, better for noisy/difficult signals
- Special: INFINITY for exhaustive search
RX filter bandwidth in HzOverride automatic bandwidth selection:
- Narrower: better noise rejection, requires accurate tuning
- Wider: more frequency tolerance, more noise
- 200 Hz for 400+ baud
- 50 Hz for 100-400 baud
- 10 Hz for under 100 baud
Exit after receiving one complete transmissionAutomatically exits when carrier is lost after first message.
Useful for batch processing or scripting.
Transmit Options
Output signal amplitudeValues:
0.0to1.0: amplitude level (1.0 = maximum)E: FLT_EPSILON (minimum possible value, for testing)
Sine wave lookup table lengthControls TX tone generation quality vs. memory:
- Larger values: higher quality, more memory
- Smaller values: lower quality, less memory
- 0: disable LUT (calculate sin on-the-fly)
Transmit continuous carrier toneMaintains carrier (idle mark tone) even when no data is being transmitted.
Useful for keeping receiver locked or testing.
Print ”### EOT” message when transmission endsOutputs end-of-transmission marker to stderr.
Audio Options
Read from or write to audio file instead of audio deviceSupports WAV, FLAC, and other formats (via libsndfile).
- TX mode: writes audio to file
- RX mode: reads audio from file
Audio sample rate in HzCommon values: 8000, 11025, 22050, 44100, 48000, 96000Higher sample rates provide better accuracy but use more resources.
Use ALSA backend with optional device specificationDirect ALSA audio device access:
- Without argument: use default ALSA device
- With argument: specific ALSA device (e.g., plughw:1,0)
Only available if minimodem was compiled with ALSA support.
Use sndio backend with optional device specificationOpenBSD sndio audio system:
- Without argument: use default sndio device
- With argument: specific sndio device
Only available if minimodem was compiled with sndio support.
Use floating-point sample format instead of 16-bit integerProvides higher precision for TX audio generation.
RX always uses float samples internally (required for FFT).
Output Options
Suppress status messagesDisables CARRIER/NOCARRIER and other status output to stderr.
Only decoded data or errors are displayed.
Filter non-printable characters in outputReplaces non-printable characters with ’.’ for display.
Useful for debugging or displaying binary protocols.
Utility Options
Display version information and exitShows minimodem version, copyright, and license information.
Run performance benchmarks and exitTests tone generation performance with different configurations.
Useful for comparing system performance.
Experimental Options
Experimental: Add noise to received signal for testing
Common Option Combinations
High Quality Transmit
High Quality Transmit
Robust Receive
Robust Receive
Fast Performance
Fast Performance
File Processing
File Processing
Custom Protocol
Custom Protocol
Option Categories Quick Reference
Basic
--tx/--rx--file--quiet--version
Encoding
--ascii/-8-7--baudot/-5--binary-output--binary-raw
Frequencies
--mark--space--inverted--auto-carrier
Frame Format
--startbits--stopbits--invert-start-stop--msb-first--sync-byte
Receive
--confidence--limit--bandwidth--rx-one
Transmit
--volume--lut--tx-carrier--print-eot
Audio
--samplerate--alsa--sndio--float-samples