[time-nuts] Linear voltage regulator hints...
alex at pcscons.com
Fri Dec 12 23:17:24 EST 2014
just thinking; OXCO is one ovenized crystal oscillator with temperature
control, better to say temperature stabilizer, thus if the outside
temperature changes the control loop shall keep the internal temperature
constant-- by definition,
the function of the temperature control loop could be observed by the
variation of the supply current of the oven. Also the reference voltage
supplied from inside of the OCXO is coming from a voltage source which
has stabilized temperature, therefore it is "a relative stabil reference
voltage source", which could be used to compare the stability of other
voltages and thus, it could be found which voltage is moving with the
On 12/12/2014 7:53 PM, dan at irtelemetrics.com wrote:
> Hi Bob,
> > or 1x10^-8 per volt. If it’s a 10 MHz OCXO.
> > That would be 1x10^-14 per uV
> > 4.7 x 10^-13 for 47 uV
> Good, so I'm not out to lunch here. ;) Thanks for verifying those
> numbers for me!
>> What makes you believe that the OCXO’s temperature performance it
> not the issue?
> Because I can blow a hair dryer on it, and make very warm - almost
> hot to the touch and not see the phase or DAC change. Yet 2 degree
> thermal cycles in the room show up in the DAC and phase. I'm pretty
> sure it's not the OCXO, but if you know anything that would suggest
> otherwise, please do share.
> > I’d guess that the analog stuff is much better than it needs to be.
> At this point I would tend to agree, but don't have hard numbers to
> know for sure yet.
>> Subject: Re: [time-nuts] Linear voltage regulator hints... --> WHY?
> > Ok, so why am I harping on the “need” for all this from a system standpoint ?
> I have no idea.
> > 1) Adding stuff to a design that does not make it measurably better
> is simply a waste of money. That’s ok if it’s your money.
> The stuff added needed to be added. It fixed an understood
> problem/limitation in the current hardware. It did make the system
> 'measurably' better.
> > 2) Others read these threads and decide “maybe I need to do
> that..”. Now it’s a waste of somebody else’s money.
> If someone makes the decision to spec their part based on a somewhat
> random email, from some random thread, from an email list, they fully
> deserve the spend the extra $6 on parts. It serves them right for being
> so foolish! (Serously?!?)
> > 3) Still others look at this and decide “If I need to do that,
> I’m not even going to start”. That’s not good either.
> This isn't extremely hard, but it is challenging. Maybe someone
> wanting to build a GPSDO should know what they're getting into. If a
> 10e-6/DegC scares them, you'd think coefficients of "1x10^-14 per
> uV" would be worse.
>> 4) Analysis *is* part of the design process. It should very much be
> part of this.
> It is. It's how the analog portion got to where it is now. What makes
> you think it isn't?
>> 5) Focusing on a design aspect “because I can” is a very common
> thing. I do it all the time :) Because I fall into the trap often, I
> recognize just how much time gets soaked up on dead ends this way.
> I'm doing this "because it's what I can easily contribute to the
> project". I'm spending considerable resources in terms of time and
> expenses studying and improving a piece of hardware to help a guy out,
> and to learn something along the way.
>> 6) There are very real issues when doing this. Sorting out what’s
> real and what isn’t is far from easy. The more “noise” in with
> the signal, the less likely others are to figure out a good approach.
> Huh? Do you mean this particular response to the thread?
> Going back to the original post, the reason for the question was to
> look for a lower cost yet suitable replacement for the 'roll your own'
> design. One that could be shotgunned into the prototype to look for the
> thermal drift that is evident, and is not coming from the OCXO. This is
> part of the analysis you so eloquently spoke about above. As it turns
> out there are no parts that good. Moving foreword with the project, the
> COTS parts don't cut it, so at this point I see no other choice than to
> build something.
> You obviously have a lot of experience in this field. I'm glad that
> people like yourself are willing to share with the rest of us. But,
> please don't assume I'm incapable of navigating the cost vs.
> performance curve for a project, or that I'm incapable of determining
> if a part is over specified. It's insulting that you think so.
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