Entry for Aug 6th, 2015
I faced with difficulties to operate the RF AM detectors.
I tried to operate the RF AM detector. In short I could not as I could not remove the saturation of the MON outputs, no matter how jiggle the power select rotary switches. The input power was 10~15dBm.
D0900761 Rev.A
https://dcc.ligo.org/LIGO-D0900761-v1
I've measured the bias voltage at TP1. Is the bias such high? And does it show this inversion of the slope at high dBm settings?
Setting Vbias
[dBm] [V]
0 21.4
2 21.0
4 20.5
6 19.8
8 18.8
10 17.7
12 16.3
14 14.2
16 11.9
18 10.6
20 11.8
22 15.0
The SURF report (https://dcc.ligo.org/LIGO-T1000574) shows monotonic dependence of Vbias from 0.6V to 10V (That is supposed to be the half of the voltage at TP1).
I wonder I need to reprogram FPGA?
But if this is the issue, the second detector should still work as it has the internal loop to adjust the bias by itself.
TP3 (Page 1 of D0900761 Rev.A) was railed. But still MON2 was saturated.
I didn't see TP2 was also railed. It was ~1V (not sure any more about the polarity). But TP2 should also railed.
Needs further investigation |