Live Testing of the Full System

A project log for Stepmotor Driver Board for TI Tiva Launchpad

Three axis stepmotor driver, limit switch conditioning and power supplies.

BharbourBharbour 08/07/2016 at 17:220 Comments

Progress on the antenna rotator project has been slow. The amateur radio sats mostly use the 2 Meter and 70CM amateur bands (or close enough). A few of the sats use FM, but Sideband (SSB) is more common. I set up the rotator outside with a netbook computer to run the satellite tracking software and control the radio (a Yaesu 857D). A couple of discoveries were made:

The satellite RF frequency information in Gpredict (the satellite tracking software that I am using) is incomplete. When there is no frequency information for a satellite, it uses whatever values were left from the previous satellite. I need to research and write the frequency information for the rest of the amateur sats into the Gpredict database files.

The theta axis step motor radiates significant RF energy when enabled. This should not be too surprising, in that there is 3 feet of exposed cable carrying the step motor phase drives. I used foil shielded cable with the shield grounded to the case of the rotator. Running the radio in SSB mode on 145.8MHz and the theta axis enabled, the radio background noise level is around S9. When the theta axis is moving, you can hear the step pulse rate in the noise on the radio. With the theta axis off, the background noise level is around S4 or S5. Disabling the Azimuth and Elevation motors does not result in a detectable change in the background noise level. Similarly, removing the power into the rotator electronics makes a very minimal change in the background noise level. I need to put some VHF/UHF filtering on the theta axis motor wiring. I checked for RF emissions from the main body with a spectrum analyzer, and did not find any. It looks like I need to repeat that process with the theta axis installed and enabled to check the effectiveness of the filter changes.

I discovered the frequency database problem late in the day, toward the end of a pass by the FO-29 sat. Manually controlling the frequency and disabling the theta axis motor, I was able to hear CW traffic from the sat, so there is progress.