[time-nuts] Surface Mount OCXO Questions

[John C. Westmoreland, P.E.]

Bob,

These are good suggestions.  I will probably end up doing 1) and 2) you
have outlined above.

Thanks!
John W.



On Thu, Oct 31, 2013 at 7:51 AM, Robert LaJeunesse <
rlajeunesse at sbcglobal.net> wrote:

> A couple tricks I've learned along the way: 1) If using a switching supply
> is required to get a higher voltage, follow it with a good LDO to reduce
> the noise level. I've done this successfully for powering handheld radio
> microphones with built-in amplification, video amplifiers, and for
> operating a GPS receiver and antenna. 2) If there is a possible ground
> current path problem, break the ground path by using a unity gain
> "difference" amplifier like the AD8276, or a difference amplifier with gain
> like the INA145. The input is differential to the source signal, and the
> output has a moderately high impedance reference terminal that can be tied
> directly to the load device ground pin. I use this technique all the time
> to keep down the noise when driving remote analog loads that have large
> ground currents themselves. (Picture a 110W 40MHz transmitter running off
> 12V, at the bottom of a stack of other transceivers in the trunk of a
> police car - with 40A of
>  lights flashing, etc.)
>
> Bob LaJeunesse
>
>
> >________________________________
> > From: "John C. Westmoreland, P.E." <john at westmorelandengineering.com>
> >To: Discussion of precise time and frequency measurement <
> time-nuts at febo.com>
> >Sent: Wednesday, October 30, 2013 10:54 PM
> >Subject: Re: [time-nuts] Surface Mount OCXO Questions
> >
> >
> >Graham,
> >
> >Good points - yes, I have this part currently in the design: TPS75833KTTT
> >(LDO from TI) - putting another one down
> >(just) for the OCXO isn't a problem.
> >
> >And a nice 12V rail isn't a problem either since this is for a radio with
> a
> >nice 12V source.  Could I boost the 3.3V rail to
> >12V or maybe 5V to 12V - sure - but your point about the switcher is well
> >taken and I agree.  Having a nice, fat, analog
> >ground plane isn't a problem either.
> >
> >And, this is just a 'dev' board so we can do what we need to make the OCXO
> >work as good as possible.
> >
> >From their spec sheet:  '... the supply voltage sensitivity and load
> >sensitivity is 5E-11 for a 5 % change in voltage or
> >load impedance.'
> >
> >Thanks,
> >John
> >
> >
> >
> >
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