To use RSPUno for interferometry
To use RSPUno for interferometry, you’ll need to understand both the hardware configuration and the software/data processing workflow. RSPUno is a system derived from the Radio-SkyPipe software but optimized for the Radio JOVE community and SDR-based systems like RTL-SDR, SDRPlay, etc. It supports single and dual-channel operation, which is essential for basic interferometry.
Here’s a step-by-step outline of how to use RSPUno for radio interferometry:
🔧 1. Hardware Setup
🛠 Required Components:
- Two identical antennas (e.g., dipoles or Yagis), spaced a fixed distance apart (baseline).
- Two SDRs (e.g., RTL-SDR dongles) tuned to the same frequency (e.g., 20.1 MHz for Jupiter/solar).
- A shared timing source (GPSDO or disciplined oscillator) for time synchronization (important).
- A computer with RSPUno installed and dual input capability (or two computers with syncing).
🛰 Antenna Configuration:
- Arrange the antennas to receive from the same source (e.g., sun, Jupiter).
- Keep the antennas well-matched and connected to identical cables and preamps if used.
- The baseline distance should be known and measurable — it determines your angular resolution.
🧪 2. Software Configuration in RSPUno
✅ Enable Dual Channel Mode:
- In RSPUno, go to the settings and select Dual Channel mode.
- Assign one SDR or input to Channel A, the other to Channel B.
- Ensure both channels are tuned to the exact same frequency and bandwidth.
- Use external clock inputs if available to synchronize timing between devices.
📐 Calibration:
- Before starting interferometry, ensure gain, phase, and delay calibration between channels:
- Use a common test signal (noise source or signal generator) fed into both antennas.
- Measure the phase/delay difference using the RSPUno oscilloscope view.
- Apply software corrections or adjust cable lengths to minimize phase errors.
📊 3. Data Collection
- Set up RSPUno to record raw amplitude or voltage data from both channels.
- Log with timestamps — ideally synchronized to UTC.
- Observe a bright source (Sun is easiest; Jupiter requires dark skies and precise pointing).
🧮 4. Data Processing for Interferometry
💡 Interferometric Measurement:
- The core of interferometry is correlation: you compare the signal from Antenna A with Antenna B to see how similar they are.
- You calculate the cross-correlation function or the fringe pattern caused by the time delay from the different antenna positions.
🧰 Tools You Can Use:
- Python or MATLAB scripts to read the RSPUno logs and calculate:
- Cross-correlation:
numpy.correlate(channelA, channelB, mode='full') - Fringe visibility and phase shifts over time.
- Cross-correlation:
- Fourier Transform to analyze frequency and phase differences.
📈 5. Interpreting Results
- From the fringe frequency, you can determine the angular position of the source.
- Varying the baseline or observing over time (Earth rotation synthesis) improves resolution.
- Plot visibility vs. baseline length to extract source size or structure (basic aperture synthesis).
🧭 Practical Tips
- Start with Sun interferometry — it’s bright, predictable, and doesn’t require night-time observing.
- Use identical antennas and cables to avoid differential phase delays.
- If synchronization is challenging, use post-processing alignment techniques based on known sources.
⚠️ Limitations of RSPUno for Interferometry
- RSPUno is not designed as a full interferometry suite (like CASA or AIPS).
- It lacks built-in phase calibration or imaging tools.
- You may need to export data to external software for deeper analysis.
🧩 Alternative Options
If you want more advanced interferometry capability:
- Use GNU Radio to capture synchronized IQ data from multiple SDRs.
- Use Python interferometry toolkits like those from SETI Institute or Amateur Radio Astronomy groups.