Modal vibration testing of the 26m John A. Galt radio telescope

The Dominion Radio Astrophysical Observatory’s John A. Galt 26m radio telescope serves multiple roles for the Canadian radio astronomy community. The attributes of this telescope make it ideal for spectropolarimetric studies of the interstellar medium, however instrumental conversion between polarization states of the incoming signal can corrupt the astronomical signal as the telescope undergoes various loading conditions. To characterize these effects, a finite element (FE) model of the telescope was constructed, based on available blueprints and supplemented by manual measurements. To validate this FE model, vibration measurements were conducted over four days in September 2022 by NRC-Herzberg engineers. The telescope was instrumented with accelerometers, and vibrations were excited using the step-release and impulse hammer methods. This paper will briefly review the model development and analytical predictions, will describe the instrumentation plan and experimental approach used, and will summarize key results from these tests, in particular the first several vibration modes of the telescope.