I second that, when done correctly, it works great. But there are all kinds of ways to do it poorly.
First off, What the TBolt is best for is to provide great long term frequency stability that can be better than a Rb or Cs. If you want a low phase noise signal without spurs, Don't use the Tbolt's output directly, use the TBolt to discipline an external low noise oscillator. The TBolt's perform can be made even better, by reducing the excess noise that it's control loop adds to the OCXO. Any noise on the DAC out, that is at a frequency higher than the control loop Bandwidth is adding noise to the Osc, not reducing it. the basic steps needed to make the TBolt as good as it can be, listed in reverse order of importance are: 1) Increase the control loop time constant. The 100 second default gives poor performance for a well setup TBolt. I find 2000 sec, using the extended TC method is about right for my stock unit. To be able to use that long of a TC, both the Antenna system and environment must be made near perfect. 2) Set the Tbolt up to be insensitive to changing room temperature The desired goal being not to let any part of the TB's case change temperature over ANY time period. Several different ways this can be done, each with it's own set of compromises. The simplest, cheapest, safest, smallest and best performing way I have found is; <http://www.febo.com/pipermail/time-nuts/attachments/20120712/9aa84ffa/attachment-0001.jpg> 3) Get a good antenna system with a good view of the sky and set the elevation low enough so that there is always at least 4 or 5 satellites being used, but still high enough not to see any sat signal that is below about 40dBm, or that has any reflections in it. I find 15-20 deg works best for my location. 4) Use a good stable power supply that does not add any low freq Osc noise. Obviously if the TBolt is bein g powered from a power supply that is jumping around due to fan switching, temperature changes or anything else, It is being done way wrong. BTW, The Tbolt is much less sensitive to changes on the -12, so if you do not want to properly isolate the + supply, use the -12 volts for the Temperature controller power. ws *********** Nope, if implemented properly it works VERY well. No ADEV humps, no vibration induced spurs, no commutator EMI, no power supply garbage. Lady Heather's PID PWMs the fan to control the speed. It is not a bang-bang controller. You should baffle the air flow so that it does not impinge directly on the unit. I have the tbolt sitting on a piece of waffle foam in the box... gives very good vibration isolation, but even without it I saw no fan related noise/spurs. Proper power supply filtering for the fan power might be useful, but I see no coupling on mine. As the Wise Man said... one experiment is worth 1000 opinions. --------------------- Sorry guys, but using a fan on a thunderbolt is nuts. Not time nuts. _______________________________________________ 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.
