In the attached, left is the trend of 45MHz signals after the driver swap in the PSL room. Signals named MOD_RF45 are from the PSL room, MOD_9MHz are actually from the old unit now installed in CER (and it's not 9MHz, it receives 45MHz signal from the 45MHz distribution amp).
Anyway, the new driver remained very glitchy for 6 or 7 hours but we don't see any correlation with the CER unit, then it became quiet for the rest of the night except three easily visible glitches. The largest one was about 0.06 counts pk-pk in the control signal.
But the old driver had good and bad period. For example the day before (middle panel) it was mostly quiet, but three days ago (right panel) it was nasty, and the largest glitch there was about 0.14 counts pk-pk.
Two things we learned so far are:
- Glitches in the PSL room unit are NOT due to the driver/stabilization circuit, as the one in CER ("9MHz") is the old one pulled from PSL yesterday and it's much less glitchy.
- Glitches are NOT from the distribution amplifier itself or upstream as the two units don't glitch at the same time.
We made a test with the CER unit by changing its output termination. Nominally, it runs into 50 Ohms. In the attached plot just before 70s the terminator was removed briefly and put back again. This resulted in a up-down glitch. Then, this was repeated around 80s. Between 200s and 210s the terminator was removed and replaced by a cable with clips attached to the end. The clips were then shorted repeatedly resulting in pairs of down-up glitches. Looking at alog 21789 and its second attachment we can see two up-down glitches—albeit at a much smaller scale.
Keita went out during a lockloss and started tapping at different points in the RF distribution chain of the 45.5MHz RF signal.
No effect:
- Tap at the outputs of the distribution amp
- Wiggling the large diameter cable that goes between racks
Effect similar to what we see:
- Wiggling the BNC cable connected to the unit in the CER (plot 1)
- Tapping the balun of the cable going to the PSL unit at the field rack (plot 2)
Effect much larger than what we see:
- Removing a terminator from an unused port of the distribution amp (plot 3)
- Tapping the N elbow in the cable run to the PSL unit at the field rack (plot 4)
Only the removal of the terminator was seen in both units. The other glitches were only seen by the unit which is fed by the tapped cable or connector.
The most sensitive point was the tapping of the elbow indicating a possible connector, cable or adapter problem nearby. We should probably redo the extension cable which was inserted to account for the phase delay.
