[time-nuts] Linear voltage regulator hints...

dan at irtelemetrics.com dan at irtelemetrics.com
Fri Dec 12 22:53:39 EST 2014


    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. 
  
 Thanks,
 Dan
  
  
  
  
  
  
  

  


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