On Sept 25th, we have calibrated the B1_PD2 and B1p_PD1 photodiodes, sending the IRIG-B output the (old) GPS receiver via a 21 meter cable and a LED in front of the photodiodes on SDB2. The Pd Audio signals have been acquired at 1 MHz during few seconds during these tests:
The timing of the B1 and B1p photodiode readout has changed by 200 µs with respect to O2. Looking at free Michelson data, it probably changed between May 18 and June 21st, hence probably after the timing upgrade of May 29th. Hence hrec timing parameter is currently not well tuned, at least for absolute timing.
The last change of hrec model parameters was done on June 20th, when we took into account the extra delay due to the aliasing filters added on the actuation Sc_Z_CORR channels. Then the next restart of hrec was on July 25th. Looking at VIM, the sensivity at low frequency was very good between 20th and 26th June, and was degraded only end of June, without any hrec modifiction in this period. Hence the apparition of the extra low frequency noise does not seem related to hrec configuration. Investigations still on-going...