[time-nuts] A couple of Tbolt questions

Tom Van Baak tvb at LeapSecond.com
Sat Jul 25 21:55:46 UTC 2009


>> Typical TAPR Thunderbolt phase noise is about -100 dBc/Hz
>> at 1 Hz, falling to about -150 at 100 Hz, with a floor just above
>> -160 beyond 10 kHz. Variations on this, and spurs, seem to be
>> a function mostly of power supply. For example, see:
>> http://www.leapsecond.com/pages/tbolt/noise.htm
> 
> Given the apparent sensitivity to the power supply that the Tbolt  
> exhibits, has anyone put any effort into optimizing the power supply  
> so as to minimize that set of effects?
> 
> ie: what is the best power supply to use to ensure maximum accuracy  
> for the Tbolt?  A couple of linear supplies?  Any particular switcher?
> 
> Tom Frank, KA2CDK

This could be done but do keep it in perspective. The talk about
power supplies is in the context of phase noise measurements
not GPSDO accuracy or stability. The latter are more a function
of TBolt design, or antenna placement, or environmental control,
etc.

I have yet to see any difference in TBolt stability from one p.s.
to another.

For most of us who use a TBolt as a precise time or 10 MHz
frequency reference the choice of power supply is less of a
concern. I suspect line/load regulation may be more important
than the number of spurs or the linear vs. switcher question.

If someone has time it would be nice to know the df/dV for
each of the TBolt +12, +5, and -12 volt inputs.

I take it it's only the guys who need to multiply their 10 MHz up
to GHz that phase noise becomes a significant issue.

/tvb




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