Amateur Radio Telescope

Team Lead

Introduction

My team set out to build an amateur radio telescope horn antenna using easily available materials and RF equipment, that can detect neutral hydrogen radio emissions at 1420.4MHz, and perform digital signal processing using existing GNUradio scripts.

We decided to build this project as part of our Electromagnetics & Applications course as it was:

  • Easy to build, relatively cheap
    • Hydrogen line systems offer a low barrier of entry
  • Educational! Provides educational opportunities in:
    • Radio astronomy and astrophysics fundamentals
    • Antenna design and fabrication
    • RF front end design
    • Lots of further development pathways to larger and more sensitive equipment (e.g. larger antenna, more sensitive electronics, dual antenna interferometry)

Simulation and Analysis

Figure 1: Farfield 3D plot
Figure 2: Farfield 2D plot

The horn antenna is simulated in CST Suite to validate its performance. Unfortunately, we were not able to obtain a satisfactory S11 (return loss) parameter due to inadequate experience with simulating very large antennas in CST.

Results

Figure 3: First light observation after plotting on Excel
Figure 4: Physical setup for observation

The first light of the instrument was achieved on 1st August 2024, with the DSPIRA Spectrometer program running on GNURadio.

What did we do well?

  • Antenna fabrication:
    • The antenna was physically more robust compared to the original DSPIRA antenna.
    • More suited to mass production due to ease of manufacture for professional metalworking shops
  • 1st Stage RF design: a good first stage design gives good leeway for future expansion

What could have been done better?

Figure 5: Frequency peak at 1420.3MHz instead of the expected 1420.4MHz
Figure 6: Original RF design (top) and the current RF design (bottom)
  • The software defined radio
    • The clone HackRF One SDR has significant spurious signals due to shoddy workmanship (possibly inadequate EMI mitigation) and component quality
    • Significant frequency shift of -0.1MHz
    • Consider external high accuracy clock source to allow for accurate quantitative measurements (e.g. Doppler)
  • Better RF design in 2nd stage
    • Since we accidentally burnt one LNA…the current setup is not ideal
    • Take advantage of LNAs that accept a DC bias voltage to reduce cabling

Further readings

This project was also presented at the Singapore Amateur Radio Transmitting Society (SARTS) quarterly meetup here.

For further resources should you wish to learn more about amateur radio astronomy and the resources that helped us build this project, please review this document.