W9KE Satellite Tracker - Project Home

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There are many fine az-el rotor controllers available in the market today. Why would anyone reinvent the wheel and design another one. The main reason is to provide support for stepper motors. It is fairly easy and inexpensive to get on the satellites. A small handheld antenna and a simple radio are all you need to get started. To move up to the linear satellites an azimuth-elevation controlled antenna is almost a necessity. There is a huge jump in cost and complexity to move up to this level. Unfortunately the amateur satellite market is very limited so there is no incentive for anyone to produce a low cost commercial az-el rotor system. The Yaesu G-5500 is currently the only viable option. It is a great piece of gear but is quite expensive and the rotor motors run on AC which makes portable option a bit more difficult.

Some hams modify TV rotors but positon control of these devices is a bit difficult. Cable and satellite TV have also made TV rotors a thing of the past so low cost rotors are somewhat difficult to obtain. Most TV rotors operate with AC motors so portable operation is more complex.

Stepper motors offer some advantages when used in rotor applications. They are easy to control, run off low voltage DC, do not need a complex high ratio gear train and do not require a brake. They do not need any extra components to determine position. They stop and hold position rather than coasting like conventional motors. They are readily available at low cost on the surplus market. They do have some disadvantages. Torque comes at a premium, they draw power constantly and they do not hold their position when power is removed from the motor as their residual torque is very low. They have only relative position control and make some noise. They also require a different type of controller. The controller part is very simple as it is nothing but a small handful of electronic parts and a little straightforward software. The mechanical aspects of the rotor is a much bigger challenge. It is difficult to produce a strong compact az-el rotor system without a CNC machine or two and foundry support. This site describes my attempt to solve this problem.

Another application for stepper motors is shown in the iPoint section of this site. This is not a business - there is nothing for sale. Enough information is provided so an experienced ham can build up the controller from readily available parts. It is a great deal of fun and very satisfying to build something from scratch that is actually useful. Since this is not a kit you are free to use your creativity and build something unique and hopefully improve on what I have done.

The controller receives data from a satellite tracking program like the excellent SatPC32 in Yaesu GS-232 controller format. Yaesu has published the details of their GS-232 format. Most satellite tracking programs support the GS-232 format so this controller should work with most tracking programs. The controller converts the heading information it receives from the tracking program into motor movement. Several people who saw the stepper controller asked about support for the Yaesu G-5500 az-el rotor system. The G-5500 is very easy to control as there is a connector on the back of the rotor control box for remote control. The remote control jack was included by Yaesu to allow use of their GS-232 Rotor Controller Interface. The extremely high price of the GS-232 (around $600 today) combined with the simplicity of controlling the G-5500 spawned a large number of compatible controllers.

The block diagram of the controller is shown below. If you are interested in controlling only stepper motors you do not need the '12 bit 2 Channel A/D Converter' or '4 NPN Transistor Switches' sections. If you are interested in controlling only the G-5500 you do not need the two stepper motor controller sections. You can build a universal controller by including all the sections shown in the block diagram. The software is able to control the steppers and the G-5500 at the same time. It is fun to have the controller run an iPoint sitting on your desk while it is moving the G-5500 outside. I guarantee visitors in you shack will be impressed.


For more information on various parts of the project click on the links at the top of the page.