If you are lucky, you may be able to get one of this used atomic frequency standard for about US$100 from ebay. This is a programmable clock from 1Hz to 20MHz. With the low phase noise of this clock, it is the best choice to create a super clock standard using FE-5680A. The supply of this clock use 15Vdc and current about 2A. After warm up for 10 minutes, the current will drop to about 0.75A. Thus the continue power consumption is about 12W which is quite a lot and thus the metal body should be attached to a heat sink or metal chassis for cooling.
Currently I am using this Rubidium Frequency Standard at 10Mhz as the reference frequency for other equipment like frequency counter or AP-2522 etc…
There are two documents that I can find from internet which are very useful for using this super low noise clock.
If I have time, I shall put this super clock into a chassis with all the connectors and power supply all in one box… It is something like a reference clock used in a studio to sync all the digital equipment.