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.
Nice set of experiments. Thanks for doing them and reporting
the results. I also found that foam insulated enclosures do not
help with ~hourly HVAC cycling. I reasoned that over the span
of half an hour there is more than enough time for the delta T
of the outside world to infect the inside temperature; thus the
foam does little or no good. If the temperature changes are
more rapid however the foam might start showing advantage.
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
It seems this would change the time constant so the loop may
no longer be optimized. But by how much is hard to say.
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.
If your instrument is fixed I don't think it matters. You'll see 10811
mounted in several different orientations in hp gear. The key thing
is not to bump or tilt the instrument (or drop it ;-). I get better results
on a concrete floor than I do in a rack or on a shelf due to vibration
and shake.
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
How about using the Rb as the TBolt LO?
I'll send you some raw TBolt 1PPS data.
/tvb
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