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Abstract:
This video captures the Open Research Institute (ORI) FPGA projects meetup/office hours from May 20th, 2025, where participants update on their progress, plans, and roadblocks. Aaron reports on implementing ORI's DVBS2 encoder and seeks resources for a Pluto SDR reference implementation. Matthew details ongoing work debugging the MSK modulator, including resolving differential encoder and decoder issues that manifested as bit errors and unexpected spectral artifacts in lab testing; he also plans to propose a hardware-level framer. Thomas provides an update on his work developing a simple link budget from the successful Venus bounce data for verification against the main analysis, and discusses a proposed photogrammetry method to measure large radio dish surfaces. The conversation expands on the application of this photogrammetry technique to understand a significant 20dB performance deficit observed with the DSES radio dish, explaining how accurately quantifying dish surface irregularities can impact link budget calculations and the feasibility of both deep space communication and radio astronomy observations.
Open Research Institute FPGA Projects Meetup - May 20, 2025
0:07 Meeting Purpose: The weekly meeting serves as an update session for Open Research Institute FPGA projects, where participants share progress, plans, required resources, and roadblocks.
0:48 DVBS2 Encoder Implementation: Aaron is focusing on implementing ORI's DVBS2 encoder and requests resources, specifically links to a Pluto SDR implementation, to use as a reference for getting OpenCI running.
2:16 Modulator Debugging & Refinement: Matthew is working through issues with the modulator, specifically a bit error anomaly seen in lab testing. This involved realizing and correcting an unintended differential encoder implementation (Massie vs. Sons from Skoon Hodgekar paper) and debugging related decoder alignment problems.
6:37 Decoder Issues: After correcting the encoder and decoder alignment, the decoder simulation initially exhibited odd behavior, only recognizing F1 symbols and not F2. While this was resolved, bit errors persist, indicating a potential issue remaining in the decoder.
10:39 Anomalies & Split Spectrum: The debugging work is intended to resolve anomalies seen in lab testing, including bit errors and the unexpected return of a "split spectrum" effect.
12:45 Venus Bounce Link Budget: Thomas is catching up on link budget work and plans to create a simple link budget based on the successful Venus bounce data next week to verify against the main Jupyter book analysis.
13:37 Importance of Real-World Data: The discussion emphasizes that research and analysis, including link budget models, must be validated against and take direction from real-world results like the Venus bounce data.
14:59 Dish Surface Measurement via Photogrammetry: Thomas asks about a proposal to measure radio dish surfaces using photogrammetry (taking many photos of marked points and reconstructing a 3D mesh via software).
15:05 Photogrammetry Explained: The host explains this method uses markers, numerous photographs from different angles, and reference points to accurately derive a mesh surface, being a cheaper alternative to LiDAR. It's used in various fields, including checking the RMS surface accuracy of radio dishes.
18:29 DSES Dish Performance Deficit: The photogrammetry method was recommended to the DSES team to diagnose a large, consistent 18-20dB performance deficit in their old military radar dish, which may be caused by the dish being deformed beyond its design specifications (e.g., expected 1.5-3mm RMS error vs. current state).
19:31 Impact on Link Budget: Measuring the actual dish surface allows calculation of the RMS deviation, which significantly impacts the system temperature and link budget via the Ruze equation, potentially explaining a large portion of the observed loss.
23:58 Focus and Dish Shape: If the measured dish shape deviates from ideal, it might require adjusting the feed (phase center/focus) to optimize performance. DSES also plans to visually confirm focus using mirrors.
27:35 Communications vs. Astronomy Needs: The 20dB loss is a more pressing issue for the DSES communication side (especially difficult links like Earth-Venus-Earth) than the astronomy side currently, as astronomy is focused on binary detection of bright sources, but this will change as they move to harder science goals requiring higher sensitivity.
28:36 Diagnosing the Loss: The dish surface measurement is another step in diagnosing the 20dB deficit, following partial improvements from replacing the feed line.
26:20 Value of Measurement Results: Results from measuring the dish surface will significantly improve the accuracy of the data class and link budget analysis by quantifying the impact of dish irregularities.