To: Edgar Castro

From: Jon Hagen

Date: 10-7-99

Subject: Monthly report for July, Aug., Sept. '99

The electrical design is now complete for a half-height turnstile junction for the 430 MHz feed horn in the Gregorian dome. This turnstile was tuned using the 3-d electromagnetic simulator program HFSS. As for bandwidth, half-height turnstile is essentially identical to the standard full height turnstile. The "match bandwidth" over which the input return loss stays below -15dB is about 50 MHz. The "polarization bandwidth" over which the ratio of left-hand to right-hand circular power is greater than 15 dB is about 20 MHz.

A complete electrical design has also been completed for the new 430 MHz collector (the waveguide carriage that will ride in the slotted waveguide under the azimuth arm and divert power into the dome). Simulations predict, as hoped, that the new device can easily operate at full power without the need for gas pressurization to avoid voltage breakdown. The bandwidth of the new design, however, is no different than that of the old collector: the -0.1 dB points are separated by about 5 MHz. The new design uses a two-stage choke arrangement that reduces the leakage (blow by) to -52 dB. Mechanical detailing of the collector and of the body of the turnstile junction will be finished in the next reporting period. These units will be built in Ithaca.

Designs were also completed for a half-height waveguide-to-coax transition, of which two will be needed in the new 430 Gregorian system, and for a 3-piece half-height waveguide calibration kit for our network analyzer. This hardware will also be fabricated in Ithaca.

The spare dome elevation motor was found to have adequate power to drive one of the tie-downs through its full range. All three tie-downs will be converted to use these larger motors. The initial efforts at lightning protection of the tie-downs increased the MTBF from lightning from about 3 weeks to more than 6 months. Recently, however, a particularly large lightning strike disabled all three tie-downs (and other systems as well). New efforts will be mounted to increase the protection of these vulnerable tie-down systems - which resemble the Benjamin Franklin kite

experiment.

The 430 transmitter required considerable maintenance during this period. The water distilling unit was repaired, the main cooling pump and pump enclosure were replaced, and a capacitor was replaced in the modulator tank. One of the lower klystron magnet assemblies has a short between two windings. An outboard power supply provides a work-around for this problem until we receive a replacement magnet being sent from Haystack. We are operating now with only one spare klystron.

The platform-mounted anemometer was built and installed. Its display/monitor unit is mounted in the control room.