@ap: Yes, reaching the usual 70GHz will be pretty much impossible with a home setup. Though the document zia posted in the first answer the used below 10GHz from a stabilized clystron. Their setup at the time was below 1ppm and was used as the Australian U standard even with only a single junction. I imagine i can update my HP5350 with an RB standard and use the output to fine tune the clystron in a feedback loop. This should give a pretty stable frequency. up to the 20GHz limit of the meter.
The decoupling from the environment iss difficult, yes. i hope, that loosely mounting the assembly on the tip of the cooler sticking inside of the UHV chamber should be sufficient though. it has to be mounted somehow anyways, even in LHe it will not experience less vibration. Also the cooling will work a bit better without atmosphere. Also i could manufacture a new tip for the coldhead made from carbon fiber, further reducing the heat transfer to the outside. That could get the Temperature down by a bit more, though hopefully its not necessary.
@BU508A: Thanks ^^ I think the nuttery is strong in me, about the rest we will see
Obtaining equipment is some times easier than thought as a student. The most expensive things are usually left over in some place. Many scientists at universities are more than happy when they see someone who is actually interested in the stuff and not only doing it for some thesis. This leads to odd situations like having a cryocompressor and coldhead in working condition, but the helium lines to connect them are missing and cost me more time to obtain than all the really expensive stuff.
about the PTB site i knew already, they are actually also referenced to in zias document, seems like ptb instructed the aussies how to do it
I just found another Site, havent read it so far, but it looks to be promising:
http://www.wikiwand.com/en/Josephson_voltage_standardIm curious how the RF is fed in and filtered later. The Australians used 6 twisted"pair" wires to get the dc measurement, probably the RF jis just not able to get through there.
EDIT: These guys did it with a cryocooler and it actually seems to be the same as the one i have
https://staff.aist.go.jp/h.yamamori/pjvs.html