Home / Radio / Satellites
Receiving & Transmitting with Satellites
Tip: Use arrow keys to tweak numbers precisely

Quick Start

The fastest path to first signals — and a safe way into satellite uplinks when you’re ready.

1) Pick a Target

Good starters: NOAA APT (137 MHz RX), ISS VHF, FM “LEO birds” on 145/435 MHz.
  • Check next passes & max elevation.
  • Note mode (FM/SSB), band(s), doppler.

2) Antenna & Front End

VHF/UHF: Yagi/Log-Periodic or Turnstile/QFH. L-band/S-band: Helix/Dish.
  • Use LNA near antenna for weak signals.
  • Keep coax short or low-loss (LMR-400).

3) Track & Tune

Follow az/el. Apply Doppler (esp. 70 cm).
  • Pre-set RX at AOS/Max/LOS freqs.
  • For TX, confirm bandplan & split.
Diagrams (replace with your images/GIF)
[Drop your LEO Yagi photo / diagram here]
[Drop your Dish + Feedhorn pic here]
Concave side faces the feed. Feed sits at the focal point in front of the dish.
[Drop your Turnstile / QFH diagram here]

Receiving (RX)

Front-end gain, noise figure, polarization, and Doppler handling matter more than raw radio power.

Front End

  • LNA at antenna (low NF) → coax → filters (if strong locals) → receiver/SDR.
  • Power LNAs via bias-tee when possible.
  • Keep connectors weather-sealed.

Polarization

  • Many LEOs rotate: circular (RHCP/LHCP) helps.
  • For linear antennas, expect fades on spin.
  • Dish feeds: choose RHCP/LHCP as required.
Filters, chokes & feedlines
  • Common-mode chokes on coax near feed & shack to reduce noise pickup.
  • Band-pass filters tame nearby pager/cell signals saturating your LNA/SDR.
  • Low-loss coax (LMR-400/600) for UHF/SHF runs; minimize adapters.

Transmitting (TX)

Start full-duplex capability early so you can hear yourself and avoid stepping on others.

Basics

  • Full-duplex (separate RX/TX paths or radios) is highly recommended.
  • Follow satellite uplink/downlink pair & doppler plan.
  • Use appropriate power; more is not always better (avoid desensitizing the bird).

Split & Doppler

  • Many FM LEOs: Uplink 70 cm, Downlink 2 m (or vice-versa).
  • Apply more Doppler on 70 cm. Step the TX VFO during the pass.
  • Mind regional bandplans and allocated modes.
Tip: Before going on-air, listen to several passes and log activity, offsets, and timing.

Antennas

Pick pattern and polarization for the band and satellite altitude. Keep the feed at the right place.

Yagi / Log-Periodic

  • Great gain for LEOs (VHF/UHF).
  • Cross-Yagi for RHCP/LHCP; switch as needed.
  • Keep elements straight; use a good balun or current choke.

Turnstile / QFH

  • Omni-ish patterns, circular polarization.
  • Excellent for weather (137 MHz) reception.
  • Accepts lower gain in exchange for coverage.

Dish + Feedhorn

  • Concave face is the front. Feed sits at the focus in front of the dish.
  • Choose RHCP/LHCP feed appropriately.
  • Focus & illumination matter more than dish size alone.
Baluns, chokes & matching
  • Current choke (e.g., several turns of coax on mix-31 core) at the feed to kill common-mode.
  • Yagis often want a 1:1 balun; some designs need specific matching (gamma/T-match).
  • Helix feeds typically don’t need a balun; match via feed geometry & groundplane.

Tracking & Control

Hand-held, manual rotator, DiSEqC motor, or full az/el rotors — pick what fits your goals.

Options

  • Manual: Hand-point a Yagi (works well for LEOs).
  • Single-axis dish motor (DiSEqC/USALS): useful for GEO arc, limited for fast LEOs.
  • Az/El rotors: proper 2-axis control for LEO satellites.

Control Ideas

  • Pre-compute az/el waypoints per pass.
  • Push serial commands to rotor/motor controller.
  • Apply rate limiting and smoothing to avoid overshoot.
[Insert your tracking GIF under this section — e.g., a smooth az/el pointer animation]

Calculators

Quick tools for Doppler, free-space loss, and a rough link-budget sanity check. (All local, offline JS.)

Doppler Shift
Positive if approaching (frequency increases), negative if receding.
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At 435 MHz, shifts are ~3× larger than 145 MHz for the same velocity.
Free-Space Path Loss (FSPL)
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Quick Link Budget (very rough)
Example: 5 W ≈ 37 dBm
Use FSPL calculator above; paste here.
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Compare against RX sensitivity / noise floor. Improving LNA NF & antenna gain helps the most.
Cross-Band Helper (uplink ↔ downlink)
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This is a helper; use the actual satellite’s published plan.

Cheat Sheet

Starter Targets

  • NOAA APT (137 MHz, RX): omni + LNA, wide FM.
  • ISS Cross-Band: VHF/UHF FM (check schedule/activities).
  • FM LEO Birds: 145/435 MHz, cross-band, quick passes.

Doppler Moves

  • More shift at 70 cm; pre-program step buttons.
  • Chase the strongest audio downlink; TX accordingly.

Small Wins

  • LNA at feed; short/low-loss coax.
  • Ferrite chokes on shack cables.
  • Weatherproof everything.

Safety & Legal

  • Licensing: Transmitting to satellites generally requires proper licensing and adherence to regional bandplans and satellite operator rules.
  • Power & EIRP: Use the minimum power necessary; avoid interfering with other users or the satellite’s transponder.
  • RF Exposure: Keep people clear of high-gain beams (especially dishes/helixes) during TX.
  • Third-party traffic & content: Follow local regulations on what can be transmitted.