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Eve (Earth Venus Earth) Signal Bouncing Project - Link Budget Review and Discussion
0:00:06 Meeting Introduction: The meeting follows an Agile-inspired format: introductions, updates on past work, plans for future work, roadblocks, and resource needs. The main focus is reviewing the link budget for the Earth-Venus-Earth (EVE) project, similar to Earth-Moon-Earth (EME) communications.
0:00:47 Project Overview: The EVE project involves bouncing a signal off Venus. This is a community effort.
0:01:38 Link Budget Review: The primary goal is to discuss the link budget, with initial contributions from the Open Information (OI) team.
0:03:11 Aaron (OpenCPI): Aaron is working on updating the MSK modulator and demodulator with the latest OpenCPI components, including I and Q samples. Focus is on simulation and hardware validation.
0:04:35 Matthew (OPV): Matthew reports ongoing work on understanding loop gain issues in the OPV project. Engaging AI chatbots (like Claude) for code analysis and suggestions, including lock detection and offset frequency compensation. Also planning to add spectral inversion capability.
0:07:07 Paul (Remote Lab): No significant progress on the remote lab, but items are on the shelf for future work.
0:08:31 Python-Based: The link budget is implemented in a Jupyter Notebook using Python, broken down into classes for organization.
0:08:40 General Parameters Class: Defines fixed parameters like frequency, power, antenna diameter, pointing/tracking accuracy, and LNA noise figure.
0:10:10 EVE Link Budget Class: Sets up functions and variables specific to the EVE mission, including Venus's radius, radar albedo, and atmospheric loss. Calculates the link budget and returns the carrier-to-noise ratio (CNR) at a specific bandwidth.
0:12:28 Distance Analysis: Visualizes the effective distance and its impact on received power and CNR. Includes calculations for both minimum and maximum Earth-Venus distances.
0:13:37 Pointing/Tracking Error: Attempts to quantify pointing and tracking errors for large directional antennas and their impact on signal loss.
0:15:06 Link Budget Calculation: Calculates the link budget based on defined parameters, resulting in a CNR of 62 dB at 100 kHz bandwidth.
0:15:55 Communications Mode Analysis, Evaluates which modulation and communication mode can work with a list of different modes.
0:17:51 Doppler Analysis: Provides a preliminary analysis of Doppler shift based on orbital velocities and rotations of Earth and Venus. The main challenge is the change in Doppler, not the absolute Doppler itself.
0:19:13 Reflection/Loss Analysis: Examines billboard versus spherical reflector models for signal reflection.
0:19:36 Mode Analysis (Incomplete): Aims to create a visualization indicating whether a specific communication mode will work ("go/no-go").
0:19:57 System Noise Temperature: Estimates system noise temperature (currently 120 K, potentially high), considering factors like pointing angle and weather conditions.
0:22:17 Mode Analysis: Plans to spend time refining the list of communication modes, referencing the WSJT-X manual (K1JT) for SNR requirements, and potentially exploring custom modes for improved system gain.
0:24:55 Introduction: Thomas, involved with the Dwingeloo Radio Telescope, expresses interest in participating in the EVE project.
0:26:18 Dwingeloo Telescope Capabilities: The Dwingeloo telescope has a 25m dish and can potentially transmit with 1 kW power (with an exception) at 23 cm.
0:27:19 Independent Link Budget Notebook: Thomas shares his own Jupyter Notebook (available on GitHub) with similar calculations, providing an independent verification.
0:29:35 Visibility and Timing: Uses Astropy to estimate Venus's visibility, noting the conjunction on March 22nd.
0:30:35 Sun Proximity: Highlights the potential issue of the Sun's proximity (8 degrees separation) causing increased noise due to antenna sidelobes.
0:31:48 Distance Calculation: Calculates the distance to Venus at the time of the experiment (42 million km, 280 seconds round trip time).
0:32:58 Link Budget Comparison: Presents similar link budget calculations, with results within 1-2 dB of Michelle's notebook.
0:34:52 Bokum Experiment Verification: Validates the calculations by comparing them to a 2009 experiment in Bokum, Germany, showing good agreement.
0:36:30 Doppler Calculation: Uses SPICE (NASA's tool) for accurate Doppler calculations, considering uplink/downlink, light time correction, and Doppler rate.
0:38:38 Doppler Spread: Focuses on the Doppler spread caused by Venus's rotation, which is difficult to compensate for. Models the worst-case scenario and estimates that 50% of the reflected power is within 1 Hz Doppler spread.
0:41:20 Power Reflection, The book Radar Astronomy by Evans and Hog Force provides graphs and formulas for power reflection at used frequency.
0:46:01 Experimental Verification, There will always be some experimental aspects.
0:52:58 Chirp Signal Analysis: Briefly discusses using chirp signals as a starting point, noting their sensitivity to frequency drift and Doppler.
0:46:44 Discussion on Doppler Spread Compensation (Matthew & Thomas):
0:46:51 Equalizer Potential: Matthew suggests the possibility of using an equalizer to "despread" the Doppler spread, similar to how equalizers are used for multipath in broadband modems. Thomas expresses interest in learning more.
0:50:11 Moon Example, Shows that Doppler spread from Venus rotation is very different from Earth-Moon-Earth libration.
0:50:17 Delay-Doppler Chart, Thomas shows an example of Delay-Doppler chart from the moon.
0:51:36 Discussion on Modulation Schemes (Michelle & Thomas):
0:51:44 OTFS Consideration: Michelle mentions orthogonal time-frequency space (OTFS) modulation as a potential custom scheme, given its representation of data on the delay-Doppler plane.
0:53:53 WSTX Mode Limitation, Thomas points out limitations with existing modes.
0:57:38 Action Items and Next Steps: Acknowledge the need to further define capabilities, understand existing modes/protocols, and identify the remaining gap.
0:57:48 Closing Remarks and Future Meeting: Thanks to contributors, invitation to new participants.
Key Takeaways:
The EVE project presents a significant communication challenge due to the distance to Venus and the Doppler effects.
Independent link budget calculations show good agreement, providing confidence in the initial estimates.
Doppler spread caused by Venus's rotation is a major concern, potentially limiting the effectiveness of some communication modes.
Exploring custom modulation schemes (like OTFS) and signal processing techniques (like equalization) may be necessary to overcome the challenges.
Collaboration and continued refinement of the link budget and communication strategy are crucial for the project's success.
The Dwingeloo Radio Telescope team is interested in actively participating in the EVE experiment.