![]() If you are perfectly on-track, the signal strength will not vary with the wobble. Now dedicate a separate receiver to listen to the beacon signal (don’t forget it has to track doppler, too), and observe the signal strength versus the wobble, you can get the tracking error. Let the diameter of the wobble circle be the 3 dB beamwidth of your antenna. One technique is to continually “wobble” your antennas in a circle around the expected pointing angle. But for the curious, there are a couple of ways this has been solved in the past, both requiring a steady signal from the satellite to use as a beacon. But there is another control loop that has been traditionally ignored: is your RF beam truly pointed at the satellite? Getting feedback to close this loop is a much more difficult problem, and fortunately an unnecessary one in ham satellite communications. Rotating the antennas to a commanded location represents one control loop. Use a tripod, don’t worry about the weather and wind, and enjoy the satisfaction of seeing your firmware moving those antenna across the sky. Browse the Internet for satellite tracking designs, or just design your own. Here’s where spinning your own design might be easier than adapting an existing rotator. Conventional rotators are designed to operate vertically. One final advantage for doing it yourself is that pressing a normal rotator into service on the elevation axis might be tricky. Heavy winds that might damage the bearings aren’t much of concern if the whole tripod topples over before the damage can be done. ORBITRON SATELLITE DISH RECEIVER PORTABLEFurthermore, some satellite tracking stations these days are portable and can be installed on a camera tripod in an hour’s time, the weatherproofing requirement all but goes away. Example of Compact El over Az Rotatorįor those people, the smaller size and less stringent requirements means that homebrew rotators are well within reach and suitable to this environment. But some people might argue that this takes the fun out of the installation. ![]() Commercial manufacturers have developed two-axis rotator combinations, such as this Yaesu model below, which is more compact and easier to setup. This simplifies the design if only because the equivalent surface area and weight of the antennas are much less. Fortunately in the case of amateur satellite communications only small Yagi antennas are needed. These rotator systems tend to be quite beefy, as HF antennas can be large. I was a little surprised to see that the rotator systems you can buy today are not very different from the ones we used in the 1980s, other than improved electronic controls. There’s been a 70-some year history of these mechanisms from back in the 1950s when Cornell Dubilier Electronics, the company you know as a capcacitor manufacturer, began making these rotators for television antennas in the 1950s. ![]() And usually a brake is required to keep the antenna pointed in windy conditions. A rotator design has to consider bearings, weather exposure, all kinds of loads, not just rotational. Most of the challenges are mechanical, not electrical - the antennas that they drive can be huge, have significant wind loading and rotational inertial, and just downright weigh a lot. It’s hard to imagine that an electric motor for rotating an antenna would be anything special, but in fact, antenna rotators are non-trivial engineering designs. The popularity of robotics, 3D printing, and CNC machines has resulted in a deluge of affordable electric motors and drivers. Let’s take a look at a typical ham satellite tracking setup and see how it all ties together. What’s left over are all the extremely important real-world details. When I first started tracking amateur satellites, computing the satellite’s location in the sky was a part of the challenge. ![]() ![]() If you want to listen to satellites, you have to be able to track them as they pass over the sky. ![]()
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