[time-nuts] Effects of noise on EFC line?

Magnus Danielson magnus at rubidium.dyndns.org
Tue Aug 5 16:36:02 EDT 2014


For EFC drive, I prefer to use a buffer fed from an "analog" power, so 
that the power line noise is not as efficiently inserted into the EFC line.

Cheers,
Magnus

On 08/05/2014 10:00 PM, Chris Albertson wrote:
> On Tue, Aug 5, 2014 at 11:36 AM, Bob Stewart <bob at evoria.net> wrote:
>
>> I've considered switching the HCT out for a 74LS365, assuming my drive levels are compatible.  Unfortunately, I don't have one "in stock", and "I'm way out of my pay grade", as they say.  I've also thought about putting a 100uh inductor in series with the EFC line.  I wonder if I'll have to isolate the 74xx365 chip's VCC through an inductor?  Any thoughts?
>
> Not just an inductor but a "low pass filter" (maybe CLC) designed
> reject anything outside the bandwidth of your control signal.  How
> often do you update the EFC?  Once per second? then your bandwidth is
> 0.5 Hz.     That EFC is very close to DC if your uP is only updating
> EFC once per second. Your filter should be physically close to the
> OCXO and have a very large time constant.  In addition to this I have
> a 0.1uF cap soldered directly to the EFC and Ground pins of the OCXO.
>
> You say you have detected 10MHz noise, but you can bet there is some 60Hz too.
>
> About Vcc, I assume each chip has a bypass that is physically right on
> the Vcc pin.  That is enough.
> Well almost.  You need a digital and an analog power supply, sort of.
> Don't power both off the same voltage regulator.  They can share a
> transformer But make sure the digital stuff has it's own power rail
> and it's own voltage reg.  Then you do the same with the grounds,
> digital and analog and tie them together at one place near the power
> supply.
>
> Tuns out these GPSDOs are way-simple now. Just a few parts needed.
> You can use a serial interface DAC to drive EFC.
>
> Chris Albertson
> Redondo Beach, California
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


More information about the time-nuts mailing list