Keita Daniel

Yesterday, a large oscillation around 1 MHz was observed on the DC readout of the PMC locking diode. The DC readout is tapped directly at the HF transimpedance amplifier with a 50 Ω series resistor, see D1002163. It is available at the rack and hooked to the trigger PD input of the field box. There doesn't seem to be any termination on the rack side! The DC level of the PMC readback was about 120 mV, whereas the ILS PD showed about 1 V. The transimpedance for the PMC locking diode is 1 kΩ, where it is 820 Ω for the ILS diode. No oscillation was observed. We also looked at the signal on the RF spectrum analyzer. But, when we tried it for the ILS, the HPO tripped. End of expedition.