To: Edgar Castro

From: Jon Hagen

Date: July 14, 2000

Subject: Report for April, May, June, 2000

The new collector (traveling waveguide probe) was fabricated in the Ithaca lab and shipped to Arecibo. Initial tests determined the return loss to be better than -15 dB, confirming the HFSS modeling program used to design the unit. The vector network analyzer was used to determine the position of an inductive stub to fine tune the unit. With the stub installed, the return loss dropped to better than -25dB. After some slight mechanical adjustments to the side rollers, the collector can be installed on the carriage house for high power tests. Once proven successful, a second unit will be built in Ithaca so that neither the carriage house nor the Gregorian will use the old gas pressurized collector.

Circuit boards have been designed for the new PIN diode drivers used in the 430 MHz radar system. These boards should be received and assembled in July.

A rebuilt klystron was received from California Tube Labs via Millstone.

Conditioning has been a slow process, but the tube has produced a maximum of 1MW output at the full 6% duty cycle. With the beam current off, the vacuum drops below 10^-7 within a half-hour or so. With the beam on, the vacuum rises to around 10^-6 with a full 6% duty cycle (less with a reduced duty cycle). As we increase the beam voltage to approach full power, the body current rises to 250 mA (the specified maximum value). A slight increase in beam voltage beyond that point results in a body current arc which trips our crowbar circuit. Our old tube and its predecessors also run at nearly the 250 mA maximum body current, but their vacuum, even with a 6% duty cycle, stays down around 10^-7. We suspect the new cathode may have some particularly slow outgassing process and plan to temporarily increase the filament power to accelerate the process.

The tie-down jacking stations have been fitted with improved lightning protection with a horizontal spar used to route the ground cables to the sides to form a Faraday cage around the motors and electronics.

Half-height waveguide sections were shortened to lengths needed to provide 430 MHz transmitting capability from the Gregorian dome. These sections were then sent to a local company to have the flanges resurfaced. In addition, several brass corrugated sections will be shortened by Litton Airtron, Morris Plain, NJ, the company that originally built them 40 years ago for the BMEWs system.

The VLBI terminal being built by Signatron in Concord Massachusetts is now complete and has passed most of the scheduled acceptance tests. We expect the unit will be shipped to Arecibo sometime in August.