To: file: timing_gen_mods.wpd

From: Jon Hagen

Date: 8-17-04

Subject: Modifications to 430 MHz transmitter timing generator

The protection circuitry was built to limit the prf and the duty factor on a pulse by pulse basis:

1. Pulses shorter than 2 usec were be stretched to 2 usec and spaces shorter than 900 usec were be stretched to 900 usec. Max PRF was therefore 1109 kHz.

2. The space following a beam pulse had to be at least 15 times the length of that pulse. The maximum duty factor was therefore 0.0625.

3. Pulses longer than 2.099 msec were truncated to 2.099 msec.

The new circuitry changes these rules to

1. In any 15.36 msec period, there can be no more than 16 pulses. If more pulse commands are received they will be ignored. The average PRF is therefore limited to 1,041 kHz.

2. In any 33.6 msec interval, the beam can not be on for more than 2.099 msec. As soon as this violation occurrs, the rest of the pulse-in-progress will be truncated. The average duty factor is therefore limited to 0.0 625.

The hardware changes to the timing unit are as follows:

Schematic page 3:

1. Component carrier E7: Change 13k Resistor between pin1 and pin 16 to 3k.

2 Component carrier E7: Change 0.1uF capacitor between pin 3 and pin 14 to .02uF.

New Schematic page (page 3a):

3. Build new PRF limiter and connect between old PRF limiter and Duty Cycle limiter.

Schematic page 5:

4. Remove connection between D8 pin 7 and D11 pin 2. Connect D11 pin 2 to D11 p in 4

(pull-up).

-----------------------------

Other changes

5. Have 'power dip' turn off the beam: disconnect pin 12 (or 13) of C11 from pin 6 of C11. Connect the newly freed pin to M14 pin 6. Connect M14 pins 4 and 5 together and then to N13 pin 11 (or to M14 pin 1 or M14 pin 2).

Change blinker caps to 1uF ceramic, resistors to 100k, diodes to shorts.