[time-nuts] 10811 foam enclosure

[EWKehren at aol.com]

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