Ham Radio

Ham Radio Protocols

Your comprehensive guide to radio frequencies, protocols, and the tools to explore them.

GMRS (General Mobile Radio Service)

• • Frequency allocation:** 462-467 MHz, 22 channels total. Channels 1-7 and 15-22 allow up to 50W, channels 8-14 limited to 5W.

• • Repeater pairs:** Channels 15-22 use +5 MHz offset (input 467.550-467.725, output 462.550-462.725).

• • Licensing:** $35 FCC registration, no examination required, 10-year term covers immediate family.

• • CTCSS/DCS:** Privacy codes prevent interference but don’t provide security - all transmissions remain receivable.

Amateur Radio Fundamentals

• • 2 meters (144-148 MHz):** Most popular VHF band. Repeater outputs 144-145 MHz, inputs 145-146 MHz with +600 kHz offset. Simplex operation on 146.52 MHz (national calling frequency).

• • 70 centimeters (420-450 MHz):** UHF band with +5 MHz offset for repeaters. Regional variations exist - West Coast often uses -5 MHz.

• • 6 meters (50-54 MHz):** “Magic band” with sporadic E propagation enabling 500+ mile contacts during openings.

• • License progression:** Technician (VHF/UHF privileges, limited HF), General (most HF bands), Amateur Extra (full privileges including exclusive subbands).

• • Exam structure:** 35 multiple choice questions, 74% passing score. No Morse code requirement since 2007.

Digital Protocols

• • Packet radio:** AX.25 protocol standard, typically 1200 baud on 2m (145.01-145.09 MHz).

• • APRS:** 144.39 MHz North America primary frequency. Transmits position, weather, messages using unconnected protocol.

• • Winlink:** Email over radio using Pactor, VARA, or packet modes. RMS (Radio Message Server) gateways connect to internet.

• • DMR (Digital Mobile Radio):** Time-division multiple access, two talk paths per 12.5 kHz channel. Talk groups enable worldwide communication.

• • D-STAR:** Digital voice with 6.25 kHz bandwidth, internet linking via reflectors.

• • System Fusion:** Yaesu’s digital mode with analog fallback capability.

Mesh Networking

• • Meshtastic:** LoRa modulation on 915 MHz (US), 868 MHz (EU), 433 MHz (Asia). Spreading factors SF7-SF12, higher SF = longer range but slower data rate. AES-256 encryption with rotating keys.

• • Hardware:** ESP32-based nodes, typical 1-10km range depending on terrain and antenna height.

• • Protocols:** Position sharing, text messaging, sensor data relay through multi-hop mesh.

• • AREDN (Amateur Radio Emergency Data Network):** High-speed mesh on 2.4/5.8 GHz using modified OpenWrt firmware. IP networking over amateur frequencies enables video, VoIP, file sharing.

• • Equipment:** Ubiquiti devices flashed with AREDN firmware. Bandwidth up to 150 Mbps depending on modulation and channel width.

ATAK Integration

• • TAK (Team Awareness Kit):** Military-derived situational awareness platform using Cursor-on-Target (CoT) messages in XML format.

• • Data sources:** GPS positions, imagery, chat, file sharing.

• • Radio integration:** APRS position feeds, voice coordination on amateur frequencies.

• • Mesh compatibility:** Operates over any IP network including AREDN mesh nodes.

• • Plugin architecture:** Supports various radios through TAK server or direct integration. Amateur radio provides backup when primary data links fail.

Software Defined Radio

• • HackRF One:** 1 MHz - 6 GHz coverage, half-duplex operation. Sample rate up to 20 MSPS, 8-bit resolution.

• • Software:** GNU Radio, SDR#, GQRX, Universal Radio Hacker.

• • Applications:** Spectrum analysis, signal reverse engineering, protocol development, interference hunting.

• • RTL-SDR:** $20-30 dongles covering 24-1700 MHz (with gaps). RTL2832U + R820T2 common chipset combination.

• • Uses:** ADS-B aircraft tracking, ACARS decoding, trunked radio monitoring, ISM band analysis.

Flipper Zero Capabilities

• • Sub-GHz radio:** 300-928 MHz coverage using CC1101 transceiver. ASK, FSK, GFSK, MSK modulations with configurable parameters.

• • Applications:** Garage door analysis, weather station monitoring, ISM device research.

• • Storage:** Raw recordings and protocol analysis for reverse engineering.

• • Additional radios:** 125 kHz RFID, 13.56 MHz NFC, infrared transceiver.

• • GPIO interface:** External radio modules and sensors. Open source firmware with active development community.

ADS-B Surveillance

• • Frequency:** 1090 MHz, Mode S transponders broadcasting position, velocity, identification, status.

• • Range:** Line-of-sight, typically 100-250 miles with elevated antenna.

• • Decoding:** dump1090 software with RTL-SDR hardware.

• • Integration:** Feeds to FlightRadar24, ADSBexchange for global tracking network.

• • Military/sensitive aircraft:** Often operate with transponders disabled or on different frequencies.

• • MLAT:** Multilateration using time-difference-of-arrival from multiple receivers enables tracking without GPS broadcasts.

Programming Procedures

• • TH-D3 offset programming:** Menu → Frequency → Offset Direction (+ or -) → Offset Frequency → Enter value → Store.

• • Memory channels:** Menu → Memory → Channel number → Store current frequency/settings.

• • CTCSS:** Menu → Signaling → CTCSS → Tone frequency selection.

• • Repeater directories:** RepeaterBook.com,​​​​​​​​​​​​​​​​