Hi,
I am setting up an LPRO in a steel box (for a little additional
magnetic shielding).
The power supply is a linear in a separate box (separate the magnetic
fields).
In the LPRO box is a 5V voltage reference (2 x LT1009) which is used
across a
pair of trim pots (coarse and fine) with two front panel jacks for a
high impedance
DVM to set the frequency trim voltage f the LPRO.
The LPRO is insulated with more than an inch of foam plastic and a
small fan
(on the outside of the box) is used to control the 1/2 inch aluminium
plate that the
LPRO is bolted to to about 38*C. The temperature control is much
better than 1/10 degree.
Inside the box is a decimal divider with outputs down to 1Hz, and a
phase detector
composed of 2 D latches (CMOS) the output of which is filtered and
fed to a strip
chart recorder or data logger.
I have a TBOLT connected to a decimal divider, so I can compare the
phase with the LPRO.
At 10kHz I get 1microsecond per month resolution ~ 2x10^12. As
errors show up
the trim voltage can be adjusted with the DVM by an amount that is
easy to calculate.
So with a bit of time and without much in the way of high precision
timing gear I hope
to be able to get the LPRO adjusted to the limits of its precision,
and I avoid the short term
fluctuations in the TBOLT output.
After a year or so I will be able to tell you how well it works.
cheers, Neville Michie
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