> More precisely, if I had two black boxes, one containing > a GPS-Rb-XTAL setup and another containing GPS-XTAL, > what measurement would you make from outside the boxes > to distinguish from one another?
Ah, clever question. Here's ten ways to distinguish them: 1) Use a scale or ruler -- the GPS-Rb-XO is likely heavier and larger. 2) A wattmeter -- the GPS-XTAL will probably use less power. 3) Thermometer -- the Rb version will likely get much warmer, maybe even requiring a heat sink. 4) Use a frequency counter -- until you connect the antenna the GPS-Rb-XO will be much more accurate. It will also warm up quicker; take less time to be on-frequency, something you can see by plotting a series of frequency readings. 5) Time interval counter or phase meter -- the GPS-Rb-XO will also be more stable, mid- to long-term. However, when you connect the antenna, the long-term stability will be about the same for both. 6) Turn-over -- if you flip the black box upside down, the Rb version will show little or no deviation. The GPS-XO version, on the other hand, will probably show a sudden deviation in phase and frequency, lasting seconds to minutes. Portable use, shock, and vibration might also reveal differences. 7) Hold-over -- remove the antenna and watch the frequency drift over hours or days. The Rb version should be ten to a thousand times better at timekeeping than the XO version. 8) Magnetic field -- (this is a guess; I've not tried it) place the black box near a strong magnetic field. The XO version won't care much but the Rb version will start to suffer. 9) Patience -- run them both for the rest of your life. The one that fails first is likely the Rb. 10) Compare the credit card receipts. ;-) /tvb _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
