[time-nuts] 10811 Extra Lagging etc

Brian O'Connor vk4gtw at bigpond.com
Fri Jun 16 21:40:53 EDT 2006

I am about to embark on construction of a GPSDO using the
Shera controller and a 05328-20027 HP board based around
a 10811-60111 OCXO.  GPS is a Jupiter-T.

Given that HP's engineers have done such a good job with
the oven and oscillator design, is there anything to be gained
by adding extra thermal insulation (lagging)?  How much
improvement (if any) can be achieved?  How much lagging
(if any) have people employed.  My shack is not air conditioned
and the HP board will probably end up in a simple metallic
enclosure.  Annual temperature extremes range from about 0
to +35 Celcius.  My workshop is not very flash and any
extra lagging would probably be confined to some bits of
foam glued together.

The HP board is labelled series 2224.  What does this mean?

I am yet to measure the VCO sensitivity, but am expecting
something around 1x10E-8 per volt.  What is a typical value for
the 10811-60111?

I note that Shera's QST article refers to using the 1 MHz
output from a HP5328A.  Is there any degradation of
performance or increased thermal sensitivity due to the use
of a HP marked 7490 (ripple counter) to divide down to 1 MHz?
Would use of a synchronous divider or the TVB PIC approach
yield a worthwhile improvement?  Shera's performance graph
shows a reasonably strong diurnal component.

I was planning on cutting the PCB track going to the earthed
end of the fine adjustment 10k pot and connecting this to the
controller. Is there a neater way to achieve this connection?


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