[time-nuts] Fury Interface Board: 5MHz needed?
SAIDJACK at aol.com
SAIDJACK at aol.com
Thu Nov 8 20:32:50 EST 2007
In a message dated 11/8/2007 16:34:16 Pacific Standard Time,
nebula at telus.net writes:
>12V supply. The thin wire has no heater current in it so all heater current
>drives the OXCO ground pin a fraction of a mV below the main board ground
>eliminating any EFC interaction. With great care I implemented the second
>approach.
>Peter
Hi guys,
here is a thought: why not use EFC parasitic ground current loops to cancel
out OCXO Tempco?
___________________
Most single oven heaters will have a significant tempco.
If that EFC tempco happens to be the inverse to the heater current, then it
should be possible to carefully select the heater-current-induced EFC-ground
voltage change to cancel out the OCXO tempco?!
In other words, if heater current increases (due to falling temperatures),
then EFC voltage will increase due to the parasitic ground loop.
If one is lucky, then the OCXO has a negative tempco that requires a higher
EFC voltage at lower temps.
Then, it should be possible to pass just the right amount of current through
the EFC ground connection to get a good tempco cancellation :) This current
could be scaled by selecting the length of the EFC ground cable for example.
Dirty, but probably effective once calibrated.
bye,
Said
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