COM Hardware

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Table of Contents

📡 Communications (COMM) Subsystem Guide

This page covers key practices, materials, configurations, and frequently asked questions related to the COMM subsystem of the BIRDS satellite project.

🔑 Uplink Detection Codes

Q: Can multiple uplink detection codes be set? How are they controlled or differentiated? Tag: Uplink

Yes, it is technically possible to set multiple uplink detection codes. However, the current BIRDS configuration uses a single uplink detection code, and this has proven sufficient for its mission requirements.

📡 Antenna Design & Assembly

1. Antenna Connection Materials

  • Wire Type: Leads from DIP resistors
  • Surface Preparation: Sanded with sandpaper

  • Connection Method:

    • Lead wrapped 1.5 times clockwise around a bolt (2 mm gap), then tightened
    • Example PhotoMOS for nichrome wire heating: AQZ102 (DIP part with bent leads for SMD mounting)
    • AQZ102 on Digikey

2. Antenna Fixture (White POM Resin)

  • Designed and processed locally (e.g., Kyushu University workshop)
  • Alternatively, use general-purpose metal manufacturing companies

3. Antenna Wire and Hole Drilling

  • Vendor: Osaka Heat Treatment Co., Ltd. (material only, not hole processing)
  • Recommendation: Use external companies for hole drilling due to breakage risks
  • Nichrome Coil: Can be handmade in the lab (no need to outsource)

🛰️ Antenna Type and Cable Management

4. Antenna Types

  • Typically monopole or dipole
  • Operate in UHF/VHF bands
  • Refer to the subsystem’s design document for exact specifications

5. Coaxial Cable Length

  • BIRDS used 180 mm cables; excess cable was tucked between the antenna board and RAB

6. Cable Routing and Fixation

  • Route: From COMM board (UHF TRX) top side (+Z) to the antenna board

  • Fixation:

    • Use tape to suppress vibration
    • During FM assembly: SMA connector torqued to 56 N·cm, a small amount of Araldite epoxy applied (avoid threading area)

🔧 Drilling Thin Elements

7. Fixing and Drilling Methods

  • Use scribing for positioning
  • Drill with wood backing; scrape rather than pierce
  • Drill press must be in good condition (check bit quality)
  • For batch drilling, use metal scrap fixtures with upper templates

📶 Amateur Band Considerations and Uplink Security

8. Frequency Use & Encryption

  • Regulation: Both uplink and downlink must benefit the amateur community

  • Kyutech Policy:

    • Uplink commands are not encrypted (encryption not permitted in amateur service)
    • Pseudo-encryption: Actual frequencies hidden (e.g., “430.XXX [MHz]”)
    • Uplink frequencies removed or masked in internal/public presentations

✅ As per UNISEC’s coordination guide, pseudo-encryption of uplinks is acceptable if command content is not publicly disclosed.

📊 Link Budget Calculation

9. Excel Tool Usage

  • Input Frequency: Row 3
  • Receiver Sensitivity: Row 31 (based on COMM board test data)
  • Reference File: 119_120_121_BIRDS-5 LinkMargin.xlsx

10. Adding a Preamp (31 dB)

  • Added in Row 28 (Downlink Summary) as Preamp[dB]
  • Adjusted signal power at LNA input by including preamp gain

⚠️ Preamp amplifies signal and noise; does not increase link margin by the full gain value.

11. Accounting for Noise

  • LNA Role: Placed close to the antenna to reduce cable loss and system noise

  • Adjustments:

    • Row 29: Cable Loss
    • Row 30: Input Noise Temperature (Kelvin)

12. Noise Temperature Calculation

  • Noise Figure (NF) to Temperature:

Galactic noise in some directions can reach ~200 K. Use this source for reference.

🧮 Formulae & Notes (For Reference)

  • Noise Temperature (T) from NF:
\[T = 290 \cdot \left(10^{\frac{NF}{10}} - 1\right)\]
  • Effective Link Margin is not linear with preamp gain due to noise figure influence

📁 Resources