If the rubidium is in lock (they have an LED or an LED driver, usually) it's so good it doesn't matter any more, not many 10's of PPB off absolute. A rub is technically a secondary standard, but they're still awfully good. Both the GPS and the rub are slow-disciplined crystal oscillators, so phase noise depends on the XO quality.
John
OK, Thanks for the replies. I'll think it through later...
My voltage "standard" is the Intersil ISL60007CIB825 which is fairly inexpensive at a rather decent precision. For resistance "standards" i buy 0.1% resistors off the shelf; the exception was a few 100Meg 0.1% resistors from the Electronic Gold Mine a while ago when those were featured. Anything higher value with (high voltage ratings mostly) needs are the Ohmite 1% (again off the shelf). "Frequency standard" is via an old HP5326B. Have had little need for a current standard, but on occasion might fake something for AC current measurements. My 3-digit DVMs are more accurate for most things than my 4-digit DVM, but in a pinch use the HP5326.
=46irst thing to do is to cobble up a temperature controlled mineral oil bath. Use a Peltier heating/cooling element, a good thermistor in a bridge, and a DC power amp to drive Peltier device. Get an aquarium air pump and make a percolation pump to prevent stagnant oil.
Then the voltage reference IC and some 1 W or larger 0.05% 5ppm resistors and all go in the oil bath. The stabilized temperature and vastly better heat removal improve the performance of the hobby standards. Be sure to provide 4 terminal connections on all of your standard resistors (well up to about 100 k-ohm).
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