Our fellow ham, E25VBE, recently unveiled an inspiring project at the Bangkok Radio Fest 2025 at Zeer Rangsit: an Antenna Radiation Pattern Visualizer. What started as an experiment with just a handful of USB RTL-SDR dongles turned into a powerful teaching tool for amateur radio, bridging theory and real-world antenna behavior.

From Idea to Working System

The project took about two months to complete. Starting with four low-cost RTL-SDR dongles (just 440 THB each), E25VBE eventually scaled up to ten devices, six of which arrived in time for the fair. These dongles act as “sniff antennas” that collect live signal data from the antenna under test.

The system is built in two parts:

• Backend Server (C#) – Runs on a PC, controls up to ten RTL-SDR dongles simultaneously, and streams signal strength (RSSI) data.
• Frontend Visualizer (HTML + JavaScript) – A modern web app that receives data via WebSocket and renders a stunning, real-time animation of the antenna’s radiation pattern. The visualization is interactive, allowing repositioning and angle adjustments to match physical setup.

Live Demonstration at the Fair

Using a 5-element Yagi-Uda antenna alongside a half-wave dipole, visitors could instantly see how radiation patterns differ. One striking demo showed a 20 dB drop in signal when the Yagi was rotated from vertical to horizontal polarization — a perfect example of polarization mismatch, visualized live!

This hands-on demonstration captivated the audience and made antenna concepts easy to grasp.

Why It Matters

Commercial systems like the MegiQ RMS sell for nearly 17,950 Euros, while this DIY solution cost only around 150 Euros. Though not as linear as commercial gear, it serves the ham spirit of DIY experimentation and education remarkably well.

The Bangkok Radio Fest Atmosphere

The event itself was full of energy and community spirit. From vintage transceiver repairs to free calibration services, NanoVNA workshops, and even 3D printing support for spare parts, the fair was a true ham gathering point.

• Free entry and free booth space meant sellers were happy, and visitors had access to affordable gear and knowledge.
• About 900 participants registered, with visitors from across Thailand, plus international attendees — including several Caucasians, a Japanese ham, and even a Malay visitor!

What’s Next for E25VBE

Never one to stop at one success, E25VBE’s next project is ambitious:

• Time Difference of Arrival (TDoA) Multilateration using 8 Pluto SDRs with GPSDO synchronization.
• The goal is to geolocate transmitters with ~100m precision based solely on RF arrival time, not SNR.
• These stations will also serve as a repeater voter system, expanding coverage of the E24CY Bangkok Repeater to fully cover Bangkok and its suburbs.

This project could take up to a year, but if successful, it will be another groundbreaking contribution to the ham radio community.

Conclusion

The Antenna Radiation Pattern Visualizer is a perfect example of what amateur radio is all about: innovation, learning, and sharing knowledge. With low-cost hardware, clever software, and a lot of passion, E25VBE has created something both educational and inspiring.

We congratulate him once again and can’t wait to see the results of his TDoA multilateration project in the coming year.

More photos and videos on E25VBE Google Drive here