An analysis of the reported oscillations of the telescope has been carried out. From the TCS log it can be seen that virtually all the ``jumps'' are in the azimuth direction. It was considered that the problem may be due to the azimuth tachometers, and the devices were examined and cleaned. Since this operation no large jumps have been reported though smaller ones are still recorded in the TCS log.

Analyzing the data by reading the TCS log and using the time when the jumps occur, the corresponding azimuth and altitude positions were extracted from the database and it has been found that since the tachometers have been cleaned all the recorded (small) jumps occur between azimuth angles 100 to 270 degrees, i.e. south. Measuring the telescope speed at the time of the jumps, they typically occur at nominal tracking rates, not specifically at high tracking rates, which was suspected.

Checking the altitude angles at the times of the azimuth jumps, roughly a uniform distribution around 42 degrees can be seen, which provides no obvious information to the cause.

Recently the wheels driving the telescope were greased. It is not clear yet if that made any difference. It might also be that replacing the amplifier (see above) will solve the problem.

Thomas Augusteijn 2009-01-15