[Daniel and Bram]

With the appearance of the laser PZT resonance in the FIBR servo loop, we made a notch filter. We measured the PZT resonance in a previous entry 3857 to be at 287.55 kHz. After some searching and going back and forth we decided to go the easy way, using a passive notch filter (schematic attached 'FIBR_PZT_NOTCH.pdf'), which Daniel already has used in the TTFSS.

By the lack of finding the right capacitors, we used a 500 pF and a 100 pF parrallel, with a 0-100 pF variable capacitor (oh and we got a 470 uH SMD inductor!). With the help of EE-Dave we managed to pack it into a pomona box.

Also attached is a discustingly bad phone photo of the measured response (the RF analyser has a naughty floppy disk drive).

All in all success. We plugged it in and it worked, we can lock the FIBR Servo with a UGF of 28 kHz (another log entry will follow when I get the data from the disk).