[time-nuts] Re: OCXO Oven design (was: E1938A phase noise improvement)

[Bob kb8tq]

Hi

The market is what dictates how fancy an OCXO gets made. Bottom 
line is that there really isn’t that big a market (and willingness to pay
for super duper TC). If indeed you could do all the fancy stuff and 
still keep the sell price below $10 then who knows ….

Bob

> On Dec 26, 2021, at 1:39 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Sun, 26 Dec 2021 13:03:24 -0500
> Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> The TC of the E1938 as reported in Rick’s papers is way past what
>> a “normal” single oven will do (like by several orders of magnitude).
> 
> Yes, but the oven itself is also a much better design than
> almost anything out there. Actually, I think that most
> single oven OCXO designs out there are rather crude[1], when
> it comes to temperature control. Just using the lessons
> learned from the E1938 design (i.e. to deliberate control
> where the temperature gradients will lie) would improve
> many of the OCXO design out there. And that's something
> that could have been done without infringing upon the E1938
> patents at all.
> 
> The only other oven design, that I am aware of, that does
> something similarly is the 860x inner oven design from
> Oscilloquartz. But, as they never mention that they control 
> gradients, I am not sure whether they were aware of that issue
> or whether that's more an outcome of design optimization.
> 
> While we are at it: One of the key points of the E1938 oven
> only mentioned in passing[2] is that lateral heat flow,
> i.e., heatflow parallel to the designed equi-temperature planes,
> needs to be zero. If it isn't zero, then the equi-temperature
> planes will bend towards the upper or lower ends of the cylinder
> and there would be a net temperature gradient over the crystal.
> The two ways how the E1938 achieves this is by using "finite
> guard rings" with a gap between the main oven mass and an
> additional heater ring along the rim of the oven to compensate
> for the heat lost there. Both are very effective, though not
> the only ways to achieve this.
> 
> If this "keep the parallel heat flow at zero" would be applied
> to more OCXO oven designs, that would already improve them quite
> a bit, without the need to go full E1938.
> 
> 			Attila Kinali
> 
> [1] E.g., the FE-405's inner oven are two resistor next to the
> can of the crystal (see attached picture stolen from Bert Kehren).
> There is not even an attempt to control the gradients or make
> the temperature over the crystal related to the temperature at
> the thermistor.
> 
> [2] "The theory of zero-gradient crystal ovens", by
> Karlquist, Cutler, Ingman, Johnson and Parisek, 1997
> http://www.karlquist.com/oven.pdf
> -- 
> The driving force behind research is the question: "Why?"
> There are things we don't understand and things we always 
> wonder about. And that's why we do research.
> 		-- Kobayashi Makoto
> <FE-405B_Osc-3.jpg>_______________________________________________
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