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Following up on the success of the low-power CW beacon built by Steve G4AQB, Ross G6GVI has been working on another portable 2m beacon transmitter, now incorporating a satellite receiver to include time and location in each message and using Frequency-Shift Keying to transmit more data at a faster rate.
This beacon operates as G6GVI-P around 144.020MHz, transmitting every minute, first sending 4FSK "Horus Binary v3" modulation, followed by a message in CW Morse (around 20WPM). The transmit power is only around 20 milliwatts.
The 4FSK can be decoded using the HorusGUI software, set for 100 baud and 244Hz tone spacing: this program will automatically calculate the distance, bearing (and elevation) from your receiver. If you can't install the program, try the new web-based decoder: https://horus.sondehub.org/
The Morse message is simply "HORUS V3 DE G6GVI/P".
If the "Upload to Sondehub" box is ticked, the decoder will automatically send the received packet to the Sondehub Amateur site, along with your received Signal-to-Noise Ratio and frequency (if you've entered your Radio Dial Freq, in the panel).
This Horus Binary 4FSK mode has been popular on 70cm for High-Altitude Balloon flights in Australia and around continental Europe over recent years, but we believe that this is the first time it's ever been deployed on 2m (particularly with the V3 mode, which was only released in January 2026).
The frequency reference is just a crystal, so the transmission will drift over hundreds of Hertz as the temperature changes. The radio is designed for use at 433MHz, so a custom low-pass filter (see below) has been fitted to reduce spurious harmonic emissions when operating at 144MHz.
The prototype (based on an ESP32 micro) was assembled from left-over bits from other projects plus an atmospheric sensor to measure temperature, pressure and humidity.
Output spectrum of 433MHz radio operating on 2m
Output spectrum with low-pass filter fitted
Portable tests took place in February 2026, from the slopes of Winter Hill above Bolton. Using just a 15cm "rubber duck" antenna, the signals were received more than 50km away by G4NOY, as well as by G6GVI down in the town centre.
The ground-track is shown below and the complete statistics from these tests may be viewed on via Grafana.
This hardware is too heavy to fly under a little balloon, but I've also assembled a lightweight version, using a TinyThing board (Arduino Pro Mini), which operates as G0BWC, sending Horus V2 at 50 baud, plus CW ident.
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