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Earth-Venus-Earth Communication Link Budget Analysis and Recommendations

• 0:00:15 Project Overview: An initiative to develop a comprehensive, open-source link budget for Earth-Venus-Earth communications using a Python (Jupyter Lab) notebook. Collaboration includes the Deep Space Exploration Society, Dwingeloo site, Stockert-Bachum in Germany.

• 0:01:09 Inferior Conjunction Focus: The project aims to continue work through the upcoming inferior conjunction (when Earth and Venus are closest) happening very soon. The goal is to develop communication proposals for the next inferior conjunction in October 2026.

• 0:02:24 Recommendations:

  • The organization remain involved, develop this link budget, and produce candidate transmissions for October 2026.
  • Collaborate with amateur sites supporting open-source publications, digital signal processing, and citizen science.

• 0:03:09 Doppler Shift Challenges:

  • Doppler shift is lowest, Doppler shift rate of change is highest when Venus is closest.
  • 0:04:40: Doppler rate of change is a significant factor in the link budget.

• 0:04:53 March 2025 Inferior Conjunction Status: The current link budget math indicates that the March 2025 inferior conjunction is deemed too challenging for successful communication.

• 0:06:06 Link Budget Summary: Initial steps show a carrier-to-noise ratio, followed by digital signal processing techniques (spreading, coherent integration, non-coherent processing).

  • 0:07:46 Doppler Spread Penalty: Venus's rotation causes signal spreading, an additional penalty not initially fully accounted for.

• 0:08:30 Integration Time Limits: The rate of change of Doppler limits the maximum coherent integration time to 1.34 seconds.

• 0:09:14 Reducing Integration Does Not Solve: Reducing integration time to avoid Doppler spread penalty also reduces processing gain.

• 0:10:49 Chip Rate Experiments: The project is exploring if adjusting the chip rate can improve the link budget, but initial results are not promising.

• 0:12:02 Recommendations (Math):

  • Traditional modes (except a narrow, high-power carrier) are unlikely to close the link.
  • 0:12:13 Reference to 2009: In 2009 a signal was bounced off of Venus by AMSAT DL and B at Bacham. * Coherent integration (e.g., Zadoff-Chu sequences) gets closer but is hampered by Doppler spread. * The goal should be communication, not just detection (detection has been done before). * 0:13:28 SIGMF File Format: Using the sigmf file format is recommended for transmission data.

• 0:14:35 Doppler Compensation Tools: Tools based on SPICE can accurately calculate and compensate for Doppler rate and Doppler, demonstrated in moon bounce experiments.

• 0:16:37 Revised Doppler Spread Estimates (Lower is better):

  • The Doppler spread is lower than initially estimated (around 20 Hz maximum, not 31 Hz) because Venus's retrograde rotation partially cancels out the apparent rotation during the inferior conjunction.
  • 0:17:48: Thanks to contributions, all credit is given to Case Basa.
    • 0:18:20, 0:18:42 Simulations were validated against historical measurements from Arecibo.
    • 0:19:36: Cumulative Doppler spread plots show that 50% of the reflected power is within a 1 Hz spread, and about 65% is within 2 Hz.
    • 0:21:50: Suggestion to base calculations on 80% of the power, corresponding to a Doppler spread of roughly 4 Hz.

• 0:23:22 Planned Transmissions (Dwingeloo, if permitted):

  • Will likely transmit a mix of CW, Zadoff-Chu sequences, and BPSK pseudo-random sequences.
  • Limited transmission window (2 hours) due to potential interference with the Galileo system.

• 0:25:28 RF Bitbanger Discussion: A user reports successfully assembling the RF Bitbanger radio but finds the audio output too low. They are attempting to build an audio amplifier.

• 0:27:01 Deep Space Exploration Society (DSES) Site Update (Rick)

  • 0:27:16 Current photo: High winds and blowing sand at the DSES site may present operational challenges.
  • 0:28:18 Precision Time/Frequency: DSES is not well-versed in precision time and frequency. A rubidium standard has been borrowed, but it's only providing frequency lock (not phase lock).
  • 0:31:11 Receiver Failure: Recent tests with 1500 watts of transmission power likely damaged the receiver's front end due to insufficient isolation. Repairs are underway.
  • 0:33:46 Transmission Duration: Transmission duration may be limited to 2 minutes to minimize the risk of further failures.
  • 0:34:51 Scheduling: Australian dishes were unavailable for this event but might participate in future attempts.

• 0:35:39 Future Collaboration:

  • Discussing the possibility of Haystack Observatory's involvement as a receiver (or transmitter) site.

• 0:39:15: Discussion of getting ATA on board.

• 0:40:43 Success in Education and Expansion: Regardless of upcoming events, the project has increased knowledge and understanding.

• 0:41:11 Bachum Experiment Anomaly: They achieved success on the approaching position, and nothing on the receding position.

• 0:44:02 IQ Data Recording: Discussion about recording IQ data. Recommendations include using established software like SDR++ or sdr-dump, and recording both transmitted and received signals for time synchronization. B210 is recommended.

• 0:49:50 Link Budget Refinements: The plan is to refine the link budget further, incorporating Doppler spread variations and making it more user-friendly and accessible.

• 0:54:38 Future Plans: Next week will be close to the actual event. Plans to have some results for Opulent Voice.