SimTX Guide/Rotators and tracking

User guidesGetting startedTransmittingReceivingStationsSatellitesRotators and trackingMap and coverageCatalog and add-onsHealthSettings and shortcutsTroubleshooting

A rotator turns an antenna. With one you can point a directional antenna at another station or follow a satellite across the sky. Tracking a satellite also corrects the Doppler shift of its signal.

Mounts

Each antenna of a ground station has a Mount, set in the station editor:

Mount	Turns	Use
Fixed	Not at all	Wire antennas, and beams that always point the same way.
Azimuth rotator	Around the horizon	Beams for HF and VHF contacts in any direction.
Az-El rotator	Around the horizon and up to the zenith	Satellites, which cross the sky.

On a rotator, Parks at azimuth (and Elevation on an Az-El rotator) is the stored heading: where the antenna points when a session starts. Satellite antennas have no mount; they turn with the satellite's attitude. See Stations.

The Rotator control

When the chosen antenna has a rotator, the Station section of the Transmit and Receive tabs shows a Rotator control. It has two modes.

By hand

Drag the dial to the heading you want. The needle shows where the antenna points; the dot on the rim is the stored heading.
Or type the Azimuth, and on an Az-El rotator the Elevation, in degrees.
Or press Aim on map. The app switches to the Stations tab and the card Aim <antenna name> appears. Click the globe or a station: the antenna turns toward that point, along the shortest path over the Earth and level with the horizon. Press Done to keep it, or Cancel to go back to the old heading.
Use stored heading turns the antenna back to its stored heading.

With the keyboard, the arrow keys turn the dial 1° at a time and Shift with an arrow 10°.

Follow a satellite

Choose a satellite under Track a satellite. The control then offers By hand and Follow with the satellite's name, and selects Follow. The rotator follows the satellite while it is above the horizon. Before it rises, the antenna waits where it will come up.

Off the air and on the air

Off the air, the heading you set is where the next session on this antenna starts.
On the air, a change reaches the running session at once, and the rotator starts turning.

The line under the control says what the rotator is doing, for example Turning to 285°, about 40 s. or Waits at 12°, 0° up until <satellite> rises.

The heading you set applies to your sessions. It does not change the stored heading; change that in the station editor.

Turning speed

A rotator turns at a realistic speed:

Mount	Azimuth	Elevation
Azimuth rotator	3° per second	Fixed
Az-El rotator	6° per second	4° per second

Each axis turns on its own, so a turn takes as long as the slower axis needs. A half turn on an azimuth rotator takes a minute.

The rotator has its stop at north. Azimuth runs from 0° to 360° and a turn never crosses north, so a turn from 350° to 10° goes the long way round, through south.

A fast satellite passing close overhead can move faster than the rotator, so the antenna lags behind it for a while near the highest point. The rotator catches up as the satellite moves away.

The beam line on the map

The globe in the Stations tab draws a line from your station along the heading of each rotator antenna you use, labelled with the heading. It moves while the rotator turns or follows a satellite. While you aim on the map, a dashed line runs from the station to the pointer.

Why the heading matters

The direction the antenna points counts on every band:

on HF, for skywave and ground wave;
on VHF and UHF, for paths along the ground;
for satellite links;
for the noise the antenna picks up.

A beam pointed away from the other station can be weaker than a simple wire. While the rotator turns, the signal rises and falls as the beam sweeps past.

Tracking a satellite

In the Station section of the Transmit or Receive tab, Track a satellite lists the satellites in orbit. Choosing one:

turns on Correct Doppler, so the frequency follows the satellite's Doppler shift;
on a rotator, selects Follow, so the antenna follows the satellite;
shows the next pass over the station.

On a fixed antenna, tracking corrects the Doppler shift but can't point the antenna. Choose Off to stop tracking. Changes reach a running session at once. Satellites explains Doppler and passes.