NOAA SAME (Specific Area Message Encoding)

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Overview

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Technical Specifications

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Frequencies and Timing

• Data rate: 520.0 + 5/6.0 = 520.833… baud
• Mark frequency: 2083.0 + 1/3.0 = 2083.333… Hz
• Space frequency: 1562.5 Hz
• Start bits: 0
• Stop bits: 0
• Sync enabled with 16 sync bytes (0xAB) for transmission
• Bandwidth: 520.83 Hz (matches data rate)

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Framing Parameters

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SAME Message Format

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1. Preamble

• 16 sync bytes (0xAB = 10101011)
• Allows receivers to achieve bit synchronization

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2. Header (Repeated 3 times)

ZCZC[ORG]-[EEE]-[PSSCCC]+[TTTT]-[JJJHHMM]-[LLLLLLLL]-

ZCZCWXR-RWT-020103-020209-020091-020121-029047-029165-029095-029037+0030-1051700-KEAX/NWS-

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Field Breakdown

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3. Audio Attention Signal

• 1050 Hz tone (EAS attention signal)
• Duration varies by event severity
• Not part of SAME data transmission

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4. Voice Message

• Human-readable weather announcement
• Standard FM audio transmission

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5. End-of-Message (EOM) Marker

ZCZCNNN

• Transmitted 3 times
• Signals end of alert

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Common Event Codes

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Weather Warnings

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Watches and Advisories

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Tests and Administrative

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Usage Examples

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Receiving NOAA SAME

# Tune radio to 162.400-162.550 MHz, pipe audio to minimodem
arecord -f S16_LE -r 22050 | minimodem --rx same

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Transmitting NOAA SAME

echo -n "ZCZCWXR-RWT-012345+0100-1234567-NOCALL/NWS-" | minimodem --tx same

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Decoding and Parsing

minimodem --rx same -f alert.wav | grep "ZCZCWXR"

minimodem --rx same 2>&1 | while read line; do
  echo "[$(date '+%Y-%m-%d %H:%M:%S')] $line"
done

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Technical Details

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Frequency Selection

• 2083.33 Hz and 1562.5 Hz are harmonics-friendly
• Fall within NOAA Weather Radio bandwidth
• Distinct from voice frequencies
• Allow simple FSK detection

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Baud Rate Precision

• Derived from AFSK tone frequencies
• Maintains precise timing for sync byte detection
• Must be exact for proper decoding

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Synchronization Method

• Produces continuous mark/space transitions
• Allows bit clock recovery
• 16 repetitions ensure reliable lock
• Distinct from typical data patterns

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No Start/Stop Bits

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NOAA Weather Radio Frequencies

• 162.400 MHz (WX1)
• 162.425 MHz (WX2)
• 162.450 MHz (WX3)
• 162.475 MHz (WX4)
• 162.500 MHz (WX5)
• 162.525 MHz (WX6)
• 162.550 MHz (WX7)

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Building a SAME Receiver

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Hardware Requirements

1. VHF Radio Receiver
   • Covers 162.400-162.550 MHz
   • FM mode with audio output
   • Scanner or weather radio
2. Audio Interface
   • Connect radio audio output to computer
   • Line-level or microphone input
   • 22.05 kHz sample rate or higher
3. Software
   • minimodem for SAME decoding
   • Audio recording tool (arecord, sox, etc.)

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Software Setup

#!/bin/bash
# Monitor NOAA Weather Radio for SAME alerts

while true; do
  arecord -f S16_LE -r 22050 -c 1 | \
    minimodem --rx same 2>&1 | \
    while read -r line; do
      if [[ $line == ZCZCWXR* ]]; then
        echo "[ALERT] $(date): $line"
        # Add your alert handling here (notify, log, etc.)
      fi
    done
  sleep 1
done

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Parsing SAME Headers

import re

def parse_same(header):
    pattern = r'ZCZCWXR-(\w{3})-(\d{6}(?:-\d{6})*)[\+\-](\d{4})-(\d{7})-(\w+/\w+)-'
    match = re.match(pattern, header)
    
    if match:
        return {
            'event': match.group(1),      # EEE
            'locations': match.group(2).split('-'),  # FIPS codes
            'duration': match.group(3),   # +TTTT
            'timestamp': match.group(4),  # JJJHHMM
            'callsign': match.group(5)    # LLLLLLLL
        }
    return None

# Example usage
header = "ZCZCWXR-TOR-012345-012346+0100-1234567-KEAX/NWS-"
result = parse_same(header)
print(f"Event: {result['event']}, Duration: {result['duration']} minutes")

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Signal Quality Requirements

• Minimum SNR: 15 dB for reliable decoding
• Frequency stability: ±10 Hz maximum
• Sample rate: 22.05 kHz recommended (8 kHz minimum)
• Audio bandwidth: 1000-3000 Hz

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Legal and Safety Considerations

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Troubleshooting

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No SAME Headers Detected

• Verify radio is tuned correctly
• Check audio levels (not too loud or quiet)
• Ensure 22.05 kHz sample rate or higher
• Wait for actual alert (may be rare)

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Garbled Headers

• Improve antenna and signal strength
• Reduce audio noise and interference
• Check frequency accuracy of radio
• Adjust audio input gain

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Sync Issues

• SAME requires precise timing
• Use stable audio sample rate
• Minimize CPU load during reception
• Check for audio dropouts

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Advantages of SAME

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Automated Alerting

• Machine-readable alert data
• Selective activation by location
• No human intervention required
• Immediate alert dissemination

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Geographic Specificity

• FIPS codes target specific counties
• Prevents alert fatigue
• Users only hear relevant alerts
• Multiple location codes per message

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Reliability

• Robust FSK modulation
• Triple redundancy (3 headers)
• Sync byte for timing recovery
• Works in noisy conditions

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Related Protocols

• Bell 202 - Similar 1200 baud FSK
• Caller ID - Another signaling protocol

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References

• NOAA Weather Radio
• SAME Specification (EIA-TIA-RS-1834)
• NWS SAME Documentation

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See Also

• Command Reference
• Audio Configuration
• Emergency Alert Systems