[time-nuts] 10811 foam enclosure

Bob Camp lists at rtty.us
Sun Jan 9 16:52:00 UTC 2011


The answer to the "how far can you go" is (as always) "that depends". 

You can tweak a 10811 balance wise to get it's thermal gain up 10X over the factory settings. You may be able to go higher, but 10 is what's been published. That will give you an oscillator who's crystal is very insensitive to temperature. Pretty much 100% of the instability you see will be from the oscillator circuit. Since the crystal may be going one way when the circuit goes the other, the performance may actually be worse with the higher thermal gain. 

The real answer is to do temperature runs and to adjust things based on the transient and stabilized performance of your part. That way you can observe data that directly relates to the thermal control system. 

If you do decide to go with the high thermal gain case, doing a quick mod to put the unit on the B (thermometer) mode is definitely the right way to do it. You get things done in a couple hours that would take weeks otherwise. 


On Jan 9, 2011, at 9:07 AM, EWKehren at aol.com wrote:

> Being a Shera Fan I finally broke down and bought a Tbolt. I experimented  
> with a foam enclosure with roughly 1 centimeter on all sides. What I found 
> that  it only increased the board temperature by 19 C. It was still as 
> sensitive to  ambient. Thanks to Lady Heater it even shows an increase of 40 mC 
> when I walk up  to it with one minute delay.. Changing to an aluminum 
> extrusion the increase is  only 7 C and the response is much slower. In its final 
> assembly it will be  inside a larger metal mass, I do not think that the 
> higher temperature of  56 C is conducive to longer life. Opinion: putting foam 
> around a 10811 will only  give you a warm feeling unless you make it much 
> larger than shown in the picture  of of KH6GRT.
> Based on the above test results I feel mass is more important. So I took a  
> aluminum enclosed dewar weighing 943 gr. and did first put a resistor in it 
> and  heated it up with 2 W. Temp. did rise to 70 C. Next I disassembled my 
> worse  10811, which is very easy, since it is a nice compact unit and 
> inserted it in  the dewar. Monitoring temp with my YSI it shows 65.2 C with 24 C 
> ambient. Power  dissipation is 1.575 W. Will track it over time before I 
> replace the 10811 with  one of my better ones for frequency tests.
> Questions to our experts: 
> A) will Removing the foam  mess with the temp. control loop 
> B) How low can total power into the 10811 be before temp control can become 
> a problem, I think I am ok now,  but once in a chassis with Shera and 
> power  and battery the temp. surrounding the dewar may become a problem.
> C) What is the preferred orientation of the unit.
> I asked already once before if any one has data on the 1 1 PPS output of  
> the Tbolt over time, since I am considering it as an alternative to a stand  
> alone GPS receiver, and if there are GPS receivers that outperform a Tbolt 
> what  is the recommendation. It will be used to control a Rb.
> Bert Kehren
> In a message dated 1/7/2011 8:22:51 P.M. Eastern Standard Time,  
> tvb at LeapSecond.com writes:
> Has  anyone experimented with the amount of insulation on a
> 10544 or 10811  oscillator? They are meant to run hot by
> design and I worry that adding any  insulation, or too much
> insulation, will either cause over-heating or limit  the ability
> of the oven control to maintain the set point.
> None of  the hp/Agilent bench test equipment that uses these
> oscillators uses  insulation. Perhaps that's a  clue.
> /tvb
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