Section 08

🛰️ Satellites

Feature

Real-time orbital tracking for 40+ amateur satellites. Know exactly when the next pass is, where to point your antenna, and how much Doppler shift to expect.

Overview

Amateur radio satellites — sometimes called AMSAT birds — are small spacecraft that carry transponders, digipeaters, or beacons accessible to licensed amateurs. Working a DX station via a linear transponder satellite is one of the most satisfying operating experiences in the hobby: your signal goes up, bounces off a spacecraft hundreds of kilometres overhead, and comes back down on the other side of the horizon.

OpenHamClock calculates satellite positions in real time using the SGP4 orbital propagation model — the same algorithm used by space agencies worldwide. Positions update every 5 seconds. No internet connection is needed once the Two-Line Elements (TLEs) have been downloaded; everything is computed locally.

The Satellites Panel

The panel lists all tracked satellites with their current status. For each satellite you see:

Map Overlays

Ground track

A dashed line on the world map shows where the satellite's sub-satellite point will be over the next orbit. The track curves because the Earth rotates beneath the orbital plane — successive passes are shifted westward by about 22° for a 90-minute low-Earth orbit satellite.

Footprint

A shaded circle centred on the satellite's current position shows the footprint — the area on Earth that has a line-of-sight path to the satellite and can therefore communicate through it right now. If your home QTH marker is inside the footprint circle, the satellite is above your horizon and workable.

The footprint size depends on the satellite's altitude: the ISS at ~400 km has a smaller footprint than AO-7 at ~1460 km. Higher orbit = wider coverage.

Understanding Doppler Shift

As a satellite approaches, its radio signals are compressed to a slightly higher frequency. As it recedes, they stretch to a lower frequency. This is the Doppler effect — the same reason a passing train sounds higher pitched as it approaches and lower as it passes.

For a satellite on 145 MHz, the Doppler shift can reach ±3 kHz at the start and end of a pass. On 435 MHz (70 cm), it can reach ±10 kHz. This means:

• At pass start (satellite approaching): receive frequency is higher than nominal — tune up slightly.
• At pass end (satellite receding): receive frequency is lower — tune down.
• At maximum elevation (satellite directly overhead): Doppler is near zero.

Supported Satellites

OpenHamClock tracks 40+ amateur radio satellites. TLEs are fetched from CelesTrak and updated automatically every 24 hours to maintain accuracy. Here is a selection of the most commonly used satellites:

Configuration

Selecting which satellites to track

Open Settings → Satellites to choose which satellites appear in the panel and on the map. Deselect satellites you never work to keep the panel focused. The ISS and SO-50 are enabled by default; the full list of 40+ can be toggled individually.

Minimum elevation threshold

Set the minimum elevation for "in pass" indication. The default is 5°. If you have a clear horizon, 5° is fine. If trees or buildings obstruct your horizon up to 15° or 20°, raise the threshold so OpenHamClock does not report passes that your antenna cannot actually reach.

Pass alerts

Enable Settings → Satellites → Pass alert to receive an audio and visual notification a configurable number of minutes before a pass begins. This gives you time to get to the radio, deploy a portable yagi, or prepare for a scheduled contact.