Vance "KV4P" Vagell's Espressif ESP32-Powered kv4p Turns Any Android Phone Into a VHF Ham Radio

Radio amateur Vance "KV4P" Vagell has designed a device for the ham on the go, the kv4p HT — a pocket-size, open source, $35 transceiver to add amateur radio capabilities to any Android smartphone.

"kv4p HT is a homebrew VHF [Very High Frequency] radio that makes your phone capable of voice and text communication completely off-grid with at least a Technician class amateur radio license," Vagell explains of his creation. "The radio simply plugs into the USB C port on your Android smartphone and transforms it into a fully-fledged handheld radio transceiver. It's small enough to fit in your pocket and take anywhere, and since it has no internal battery it's the perfect radio to put in a go-bag or your car's glove compartment."

The hardware itself is based around an Espressif ESP32-WROOM-32 development board connected to a low-cost DRA818V radio transceiver. There are none of the parts you'd expect to see on a mobile radio rig, with no buttons, no display, nor even a tuning dial: everything is designed to be controlled using a companion app for Android smartphones and tablets, over a USB cable that also powers the radio.

Vagell released an initial closed beta of the project back in late September, before opening it up more widely earlier this month. Everything he has developed is open source, from the smartphone app to the carrier PCB that takes the microcontroller and transceiver — though this latter design has been revised to improve its filtering of harmonics, with tests awaiting delivery of an updated prototype. "It's up to you if you want to wait for this revision with better filtering," Vagell writes, "but I recommend it."

Those building a kv4p HT will find a range of impressive functions, including the ability to carry out APRS text messaging over a built-in 1,200-baud modem, 44kHz eight-bit audio with filters and squelch support, unlimited memories, a one-watt transmission power, and accessibility features including live closed captioning of voice conversations on supported phones.

More information on the project is available on Vagell's website, with source code and design files available on GitHub under the reciprocal GNU General Public License 3.