kv4p HT: Open-source 1W ham radio that turns an Android phone into a transceiver

kv4p HT is a DIY 1-watt VHF or UHF radio module that plugs into an Android phone’s USB-C port, converting it into a handheld ham transceiver. The hardware is built around an SA818 radio module on a custom PCB, draws power from the phone, and relies on the phone for its display, GPS, and battery. Everything is GPL3 licensed, including the Android app, ESP32 firmware, PCB designs, and 3D-printed case files.

The project targets amateur radio operators with soldering skills rather than consumers, requiring at least a US Technician class license. Beyond standard voice, it includes a 1200-baud modem for SMS-style text messaging and APRS-style position beaconing, plus software features like live closed captions and haptic-feedback PTT. Builders can buy a kit or source components individually, with assembly described as a six-step process.

The appeal is full ownership of the radio stack: open hardware paired with an open mobile UI, off-grid operation, and a form factor suited to go-bags. It illustrates the continuing crossover between maker culture, open-source software, and amateur radio, where smartphones increasingly act as the user interface for low-power RF hardware.