To: Edgar Castro

From: Jon Hagen

Date: 1-18-99

Subject: Monthly report for Dec. '98

The overspeed limiter was installed on the Gregorian and has been working

without false alarms. It can be connected into the emergency stop loop any

time. The second unit (for the carriage house) will be shipped from

Ithaca. Its control box will be assembled at Arecibo.

A comprehensive project was begun to put the 430 Transmitter in top shape.

The goal is to improve reliability and bring the transmitter back to its

full 2.5MW rated output power. The project will consist of:

1. Updating and redrawing the schematic diagrams of all the various

transmitter circuits (modulator, crowbar, etc).

2. Updating the instruction manual.

3. Spice Analysis of the modulator circuit.

4. Functional tests of all interlocks and control circuits.

5. Recalibration of monitoring circuits: voltage and current metering,

directional couplers, etc.

6. Complete check and calibration of the waveguide and platform mounted

components.

In addition, we should consider rebuilding the dummy load in order to

better measure the peak power output of the transmitter. The present dummy

load is capable of absorbing the full 150kW average power. Power is

measured via flow calorimetry. But when this dummy load is used, a salt

must be added to the cooling system. To resume normal operation, the salt

must be carefully flushed out. A more useful dummy load would be a low

power unit, say 20 to 50 kW, since it suffices to measure the power at a

low duty cycle. This load would have its own small cooling system. A very

accurate load could be built in the form of a large bolometer head: The RF

dummy load would have an identical companion load. The companion would be

heated by ac power, controlled with a Variac. When there is no temperature

differential between the two loads, the ac power (volts x amps) is

identical to the RF power.

Steps 1 and 2 should be done by the middle of February. Steps 4,5,and 6

will require approximately 4 months. A new dummy load system could be made

in 2 to 3 months.