EFOS-3 is the third of 12 masers made by the Neuchatel Observatory/Oscilloquartz from the early 80's onwards. EFOS is an acronym for "Etalon de Frequence Oscilloquartz". It was followed by EFOS B (1990) and C (1995), and then by the current iMaser-line at T4Science, who acquired the technology and core team from Neuchatel Observatory in 2006. To date, more than 100 masers in the "family" has been built. EFOS-3 was initially installed at Wettzell along side EFOS-1 around 1983, but was later replaced by a newer maser.
As of 2016 several of the masers are still going strong:
Each of these early masers was hand made, as evidenced by the construction drawings and parts-lists, many of which are hand written in pencil! Manuals for EFOS-2 is here. EFOS-3 was substantially rebuilt in 1994.
My story with EFOS-3 started in february 2016, while on holiday in the Canary Islands. Enjoying a beer in the sun, blessed with grandparents taking the kids for a couple of hours, I was reading Audoins "The Measurement of Time". With my 40th birthday looming on the horizon, I decided it was about time to have a midlife crisis, now seemed like as good a time as any. I have never been partial to sportscars, so I started toying with the idea of getting a passive hydrogen maser - the thinking being that these are significantly cheaper than Active Hydrogen masers, and should therefore be easier to track down used. Emails were sendt.
There are not really many companies dealing with Hydrogen masers, and of those only one got back to me - T4Science in Neuchatel, Switzerland. After a few emails going back and forth, it came up that they have this old active maser in the back. It was retired from a VLBI station, and it had been sitting in storage for a couple of years. While "cheap" is not the first word that springs to mind, it was within what could be financially feasible. Negotiations with the wife ensued.
A couple of months later, I travelled to Neuchatel to have a look at the maser, and get a little training for a few days. We exchanged the ion-pumps, replaced the caps in the powersupplies, and a few other things that needed attention. And, of course, measurements were taken. The ADEV was well within spec; starting at 1E-13 at 1 second, and dropping down to the mid E-15's. The curve starts going up rather quickly, but the measurements were taken with the top cover off, in a room with no climate control, and insufficient time to stabilise the temperature. All in all I'd say pretty good!
The phase noise is not anything to write home about, and the short term ADEV (below Tau ~.6s) is better with the BVA free running, so presumably the PLL needs some care. I made an attempt to change the timeconstant while I was there, but was ultimately unsuccessful. It is still on my list of things to do.
Purple is free-running BVA, teal is locked to cavity. The PLL is running at 5.7kHz, clearly seen
I wish I could share photos of their whole operation. It was time-nut heaven! More Rubidium-clocks than you could shake a stick at. Spaceflight qualified masers? Yep. I can not even begin to list all the interesting things I saw. Really a nice bunch of people too. Exceptionally knowledgable, helpful and friendly. I must say I had the best 4 days I can remember - pure selfish nerdery from morning to night!
Having received the prerequisite blessing from the wife, I decided to buy EFOS 3. As this particular spring and summer was exceptionally busy, I was unable to take a week off from work (and kids) and drive to Neuchatel to pick up the maser - a 3800km drive. T4Science kindly arranged for transport, to be delivered July 7th. Scheduling was tight and literally 15 minutes after a truck from IKEA had offloaded 1.6 metric tons of flatpacked furniture all over our new house, another truck rolled in to my front yard..
EFOS 3 was operational while we were still sleeping on mattresses on the floor and eating off a cardboard box! Time-nuttery at its finest, if I do say so myself..