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White Rabbit Switch PPS-output test

We got some White Rabbit Switches and I did an initial test of the pulse-per-second (PPS) output stability. In contrast to earlier measurements that showed 200ps or so of white phase noise, the PPS output on the WRS now seems a lot more stable. For various reasons the noise-floor (red data) of our 53230A time-interval-counter is at around 50e-12 @ 1s, and the WRS PPS output is at very much the same level of stability. Another 53230A counter shows about 13 ps standard-deviation for a cable-delay measurement - so I may redo these measurements with that counter. In any case a real evaluation of the short-term stability requires a DMTD measurement at 10 MHz.

53230A counter input channel fix

Update: after the fix the counter seems OK again. 12 ps standard deviation (61k PPS-pulses, collected over 17 hours) on a cable-delay test:


A broken CH1 input trace seems to be a common problem on the Agilent/Keysight 53230A counter. This is the second unit with the same problem we have seen.

The fix is to bypass the broken trace with a wire directly from the center of the input-BNC to the next unpopulated SMD-pad.

Dwingeloo Radio Telescope

I attended a VLBI-meeting at Groningen and had a chance to see the Dwingeloo radio telescope at JIVE.

The telescope is now run by amateurs and among other things they do moonbounce experiments.

20141111_122107 - 20141111_122124_blended_fused


Clock Laser beat-note

Here's the beat-note, as seen on a spectrum analyzer, between a red laser at 445 THz (or 674 nm, if you prefer wavelengths instead of frequencies) and a femtosecond frequency comb. The frequency comb has evenly spaced (100 MHz in our case) 'teeth' at well-defined multiples of RF-frequencies that we can lock to a H-maser. This allows absolute frequency measurements of the optical frequency at 445 THz. Currently we are trying to improve the SNR of the beat-note so that a frequency-counter will give a stable output reading of the beat-note frequency. The video shows about 20 dB of SNR using 10 kHz RBW (if you are optmistic), but reliable counting requires around 25 dB SNR using a 100 kHz RBW.

This laser will be used as the 'clock-laser' in our  ion-clock where it is used to drive a narrow clock-transition of a single laser cooled Sr+ ion. Earlier I blogged about measuring the thermal expansion of the optical cavity that is used to stabilize the laser.

Viikin Vitonen #22

Viikin vitonen 5k race today. +2C and a bit windy. 22:52 or 4:33/km. 1km splits: 4:26-4:30-4:31-4:39-4:37. Maybe slightly too fast in the beginning which made the 4th and 5th kilometre hard.

Here are some views from the area:

Rack PC Build - Part Two

Another rack-PC put together this week. Intel X99-chipset with LGA2011-3 CPU socket. Only PCI-e slots, no legacy PCI-slots.

Again I didn't get the polarity of the HDD-LED and Power-LED wires right on the first try. How come the industry cannot agree on a standard connector for the bundle that has the power-switch, reset-switch, HDD-LED, and Power-LED?

Another glitch was that this board has 8 slots for RAM, and the two RAM-sticks I got need to be installed exactly in the right slots - otherwise it won't even boot into the BIOS. Some reading of the motherboard manual was required.

After installing Ubuntu 14.04LTS (from USB-stick! No CD/DVD required) the NVIDIA-drivers (for the GTX750TI) were not automatically detected. I downloaded the latest driver from NVIDIA and installed it manually. This requires logging in to a text-only console (CTRL-ALT-F1), and then killing X for the duration of the install (sudo service lightdm stop)

op-amp PID controller

Here's an old-school PID controller based on simple op-amp circuits that I put together a week or so ago.

Espoorastit Mikkelä

The last Espoorastit and fitness-orienteering event for this year. But there might be some city-sprints during the winter.

Pretty steady going with no major mistakes. Control #6 is the best split, the others look pretty bland, but the overall result is good since I am 16th out of about 100. The long straight path south of the #2-#3 line would maybe have been faster and easier. I almost ran past #8 before turning back. Close to #11 it was hard to tell where I had crossed the path+river.


Rack PC build

I assembled this new PC for use in the lab.

Itärastit Latokartano

This was the last itärastit event for this year. See you next year in April again!

#2: wrong direction and slow pace out of #1 is probably the cause of the bad split.

#4: completely lost it when almost inside the control circle. Through to the big road and even ran along the road in the wrong direction for a bit...

#11 down the hill too much to the north, then looked for the control in the wrong place before I found the bend in the road,

#15 tried to look for the path marked with a thick dashed line, but there are many paths and it's not clear which one to follow. Might have been faster to simplify the plan and run to the big road behind #10 first.