----- Original Message ----- From: "Bruce Griffiths" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Wednesday, August 06, 2008 10:43 AM Subject: Re: [time-nuts] Power supply for Thunderbolt
> David C. Partridge wrote: >> I'm using the Meanwell T30-B, but Tom van Baak's test on this shows >> a bit of >> phase noise at 1Hz offset which is a tad nasty: >> >> http://www.leapsecond.com/pages/tbolt/noise.htm >> >> I'm wondering if this can be reduced with a bit of extra >> de-coupling on the >> 5V supply, but haven't got round to scoping the 5V supply to see >> what >> happens every second (presumably as the output is sent to the >> serial port). >> >> Cheers >> Dave >> >> > Dave > > If phase noise at 1Hz offset is a problem you will probably need a > power supply filter with cutoff frequency well below 1Hz to make any > discernable difference. > Since the an RC filter will produce a voltage drop in the 5V supply > the > resistor value will have to be kept small and the capacitor value > correspondingly large (several farads). > It may be possible to stack 3 low ESR super capacitors in series > (maximum voltage rating is around 2v -2.5V those with higher ratings > are > actually series connected stacks) to do this but this is a > relatively > expensive proposition. > > Alternatively a modified version of the Wenzel active power supply > filter could be used if a series stack of 2 low ESR supercaps were > substituted for the capacitor connected from the supply to the > transistor base. The modified circuit stabilises the transistor's > effective emitter resistance and keeps the active filter dc current > low. > > It may also be possible to use a variation of Wenzel's opamp > augmented > active filter scheme, however the filter low frequency cutoff will > have > to be well below 1Hz for it to be effective. > > Bruce It would be interesting to see how the 'red panel' Thunderbolts (the packaged type that run from an included switching supply fed from 24 VDC) perform under a test regime such as that TVB used to compare various three rail power supplies. In 'distant past' posts, maybe 18 months back, it was suggested that this supply is a particularly good performer, but IIRC no data was supplied to support this statement. Anyone able to oblige? DaveB, NZ _______________________________________________ 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.
