To: Edgar Castro

From: Jon Hagen

Date: 7-17-99

Subject: Monthly report for May and June '99

Mechanical modifications were completed on the carriage house over-speed limiter and

it has been in service for several weeks with no problems.

Data transmitter and receiver units were designed and built to allow the installation of a platform-mounted anemometer. These units have battery backup so that wind speed and direction measurements will not be interrupted by a power failure. The circuit cards were wired in the Ithaca lab. The unit should be installed in the next reporting period.

The 430 MHz collector (the waveguide elbow/twist that rides in the slotted waveguide under the azimuth arm) was severely damaged due to a mechanical misalignment when the line feed was repositioned to improve its focus.. A spare collector was installed while the damaged collector is being repaired on site. A new collector is being designed, not to be less susceptible to mechanical damage, but to operate without gas pressurization. The present (original) design has a complicated internal structure with electric fields high enough that sulfur hexaflouride must be used to prevent arcing. Maintaining this gas pressure is time consuming and expensive. The new design, based on finite-element modeling with a commercial program, HFSS (High-Frequency Structure Simulator), has a very simple internal structure and the modeling indicates that, in open air, it should operate at powers up to several times the 2.5MW power of our 430 MHz transmitter.

HFSS is also being used to design a turnstile junction for the 430 MHz feed horn in the Gregorian dome. It seems that there is sufficient space around the feed to accommodate a fairly standard turnstile. The modeling program confirms the designs of the carriage house and S-band turnstiles so well that it should not be necessary to build a scale model for the new turnstile - which will differ only in the diameter of the circular output waveguide.

Mechanical adapters will be made to adapt the tie-down jacks to servo motors identical to those used to move the Gregorian dome. These motors have the torque required to drive the jacks when the tie-down tensions are near their maximum values.