Documentation Index Fetch the complete documentation index at: https://mintlify.com/kamalmostafa/minimodem/llms.txt
Use this file to discover all available pages before exploring further.
Practical examples covering common minimodem use cases.
Basic Communication Simple Text Transfer Transfer text between two computers using audio:
echo "Hello from computer A" | minimodem --tx 1200
Output: ### CARRIER 1200 @ 1200.0 Hz ### Hello from computer A ### NOCARRIER ndata=22 confidence=2.145 ampl=0.850 bps=1200.00 ###
Interactive Chat Type messages in real-time:
# Start transmitter (type and press Enter for each message) minimodem --tx 1200 # On another computer/terminal minimodem --rx 1200
Press Ctrl+D to end transmission.
File Transfer Send a Text File # Transmit cat document.txt | minimodem --tx 1200 # Receive minimodem --rx 1200 > received_document.txt
Send Binary Data Transfer any file type:
cat image.jpg | minimodem --tx --binary-output 1200
For binary files, verify data integrity with checksums: md5sum original.jpg received.jpg
Large File with Compression Compress before transmission:
# Transmit gzip -c largefile.dat | minimodem --tx 1200 # Receive minimodem --rx 1200 | gunzip > largefile.dat
Audio File Processing Record and Decode Later Record audio first, decode later:
# Record transmission to file (using arecord, sox, or similar) arecord -f S16_LE -r 48000 recording.wav
minimodem --rx --file recording.wav 1200 > decoded.txt
Create Audio Files Generate audio files from data:
# Create WAV file with encoded message echo "This is a test" | minimodem --tx --file message.wav 1200 # Play it back later minimodem --rx --file message.wav 1200
Batch Process Multiple Files Decode multiple recordings:
#!/bin/bash for file in recordings/*.wav ; do echo "Processing $file ..." minimodem --rx --rx-one --file " $file " 1200 > "${ file % . wav }.txt" done
Radio Communication Amateur Radio RTTY Classic radioteletype:
echo "CQ CQ CQ DE W1ABC W1ABC K" | minimodem --tx rtty
HF Radio with Custom Frequencies Use specific mark/space tones for radio:
# USB mode, 1000/1200 Hz shift minimodem --tx -M 1000 -S 1200 300 # Receive with matching settings minimodem --rx -M 1000 -S 1200 300
NOAA Weather Radio Decode SAME alerts from weather radio:
# From radio connected to sound card minimodem --rx same # From recording minimodem --rx --file weather_alert.wav same
Example output:
ZCZC-WXR-012345-678901+0123-1234567-NNNN-
Telephone/Modem Emulation Caller ID Decoding Decode phone caller ID:
# Record caller ID signal from phone line # (requires appropriate audio interface) minimodem --rx callerid
Bell 103 Modem Emulate classic 300 baud modem:
# Transmit at 300 baud (Bell 103) cat data.txt | minimodem --tx 300 # Receive minimodem --rx 300 > received.txt
Advanced Configurations Custom Protocol Implement a custom FSK protocol:
# 7-bit data, 2 start bits, 1.5 stop bits, custom frequencies minimodem --tx -7 --startbits=2 --stopbits=1.5 \ -M 2200 -S 1200 600 # Matching receiver minimodem --rx -7 --startbits=2 --stopbits=1.5 \ -M 2200 -S 1200 600
High-Speed Transfer Push to higher baud rates:
# Try 2400 baud (requires good audio path) minimodem --tx 2400 minimodem --rx 2400 # Or even 4800 baud minimodem --tx 4800 minimodem --rx --bandwidth 300 4800
Low-Speed RTTY Variants Custom RTTY-like modes:
# 50 baud Baudot minimodem --tx --baudot 50 # 75 baud with custom shift minimodem --tx --baudot -M 1445 -S 1275 75
Testing and Debugging Loopback Test Test with audio loopback:
# Terminal 1 echo "test" | minimodem --tx 1200 # Terminal 2 (with audio looped back) minimodem --rx 1200
On Linux, use PulseAudio module-loopback: pactl load-module module-loopback latency_msec= 1
Frequency Verification Check actual frequencies in use:
# Generate test tone and inspect with spectrum analyzer minimodem --tx --tx-carrier 1200 # Use sox or other tool to visualize rec -r 48000 -c 1 test.wav & minimodem --tx --tx-carrier 1200 # ... stop after a few seconds sox test.wav -n spectrogram
Signal Quality Testing Test different confidence thresholds:
# Very sensitive (may have false detections) minimodem --rx --confidence 1.0 1200 # Normal minimodem --rx --confidence 1.5 1200 # Strict (clean signals only) minimodem --rx --confidence 3.0 1200
Noisy Channel Simulation Test robustness:
# Add background noise to recording sox recording.wav -p --norm | \ sox -m - noise.wav noisy_recording.wav # Try to decode minimodem --rx --file noisy_recording.wav \ --confidence 2.0 --limit 3.5 1200
Scripting Examples Automated Data Logger Continuously log received data:
#!/bin/bash LOGDIR = "logs" mkdir -p " $LOGDIR " while true ; do TIMESTAMP = $( date +%Y%m%d_%H%M%S ) LOGFILE = " $LOGDIR /data_ $TIMESTAMP .txt" echo "Listening... (log: $LOGFILE )" minimodem --rx --rx-one 1200 > " $LOGFILE " 2>&1 # Add small delay before next listen sleep 1 done
Error Correction Wrapper Add simple error detection:
#!/bin/bash # tx_with_checksum.sh data = " $1 " checksum = $( echo -n " $data " | md5sum | cut -d ' ' -f1 ) echo "${ data }|${ checksum }" | minimodem --tx 1200
#!/bin/bash # rx_with_verify.sh received = $( minimodem --rx --rx-one --quiet 1200 ) data = $( echo " $received " | cut -d '|' -f1 ) rcvd_sum = $( echo " $received " | cut -d '|' -f2 ) calc_sum = $( echo -n " $data " | md5sum | cut -d ' ' -f1 ) if [ " $rcvd_sum " = " $calc_sum " ]; then echo "OK: $data " else echo "ERROR: Checksum mismatch" exit 1 fi
Retry on Failure Automatically retry failed receptions:
#!/bin/bash MAX_RETRIES = 3 for i in $( seq 1 $MAX_RETRIES ); do echo "Attempt $i of $MAX_RETRIES ..." if timeout 30 minimodem --rx --rx-one 1200 > output.txt 2>&1 ; then if [ -s output.txt ]; then echo "Success!" exit 0 fi fi echo "Failed, retrying..." sleep 2 done echo "All attempts failed" exit 1
Integration Examples With GNU Radio Pipe to/from GNU Radio:
# Receive from GNU Radio flowgraph # (flowgraph outputs audio to stdout) ./gr_flowgraph.py | minimodem --rx --file /dev/stdin 1200
With netcat Network to audio bridge:
# Receive from network, transmit as audio nc -l 12345 | minimodem --tx 1200 # Receive audio, send to network minimodem --rx 1200 | nc remote_host 12345
With socat Serial port bridge:
# Serial to audio socat /dev/ttyUSB0,raw,echo=0,b9600 - | minimodem --tx 1200 # Audio to serial minimodem --rx 1200 | socat - /dev/ttyUSB0,raw,echo=0,b9600
Real-World Scenarios Emergency Communication Air-gapped data transfer:
# Computer A (no network, has speakers) cat emergency_message.txt | minimodem --tx 300 # Computer B (no network, has microphone) minimodem --rx 300 > received_message.txt
Use 300 baud for maximum reliability in difficult conditions.
Data Over Intercom Send data through building intercom system:
# Transmit (into intercom) echo "Door code: 1234" | minimodem --tx --volume 0.6 300 # Receive (from intercom speaker) minimodem --rx --confidence 2.0 300
Acoustic Data Transfer Air-gapped systems or underwater communication:
# High-volume transmission minimodem --tx --volume 1.0 300 # Sensitive reception minimodem --rx --confidence 1.8 --limit 3.0 300
Radio Beacon Continuous identification beacon:
#!/bin/bash while true ; do echo "BEACON ID:W1ABC GRID:FN42 $( date -u +%H%M)Z" | \ minimodem --tx rtty sleep 300 # Every 5 minutes done
Low-Latency Mode Minimize decode latency:
minimodem --rx --limit 1.5 --confidence 1.2 \ --samplerate 22050 1200
High-Quality Recording Maximum quality for file output:
cat data.txt | minimodem --tx --file output.flac \ --volume 0.8 --lut 8192 --float-samples \ --samplerate 96000 1200
Low-Resource System Minimize CPU/memory usage:
minimodem --rx --samplerate 22050 --limit 2.0 1200
Troubleshooting Examples Too Many Errors Increase robustness:
# Reduce baud rate minimodem --rx 300 # instead of 1200 # Adjust confidence minimodem --rx --confidence 2.5 --limit 3.5 1200 # Narrow bandwidth minimodem --rx --bandwidth 100 1200
No Carrier Detection Diagnose frequency issues:
# Try auto-detect minimodem --rx --auto-carrier 1200 # Check inverted minimodem --rx --inverted 1200 # Reduce confidence threshold minimodem --rx --confidence 1.0 1200
Audio Level Issues # Increase TX volume minimodem --tx --volume 1.0 1200 # Check audio levels arecord -D default -f S16_LE -r 48000 -c 1 test.wav aplay test.wav # Listen for proper level
See Also
Overview CLI basics and syntax
Modes Transmit and receive modes
Options Complete options reference