[ntp:questions] how do I lock in average frequency correction

Chris Albertson albertson.chris at gmail.com
Mon Feb 13 20:25:51 UTC 2012


On Mon, Feb 13, 2012 at 10:59 AM, Chuck Swiger <cswiger at mac.com> wrote:

>>> You might be able to improve the stability of the crystal by ensuring good
>>> airflow and cooling via HVAC as needed.  And I suppose you could adjust the
>>> rate by changing the HVAC set-point, but I don't think the benefit is worth it.

For temperature stability, I just finished building a fan controller.
 There is a temperature sensor on the end of a 18" cable.  Glue the
sensor onto anything you like.  Then when the sensor matches a set
point the fan comes on.    I think this should work as long as you
keep the set point above the room temperature.     I've not tried it
yet.  It is simple enough to make.  The TMP36 sensor outputs a voltage
of 10mV per degree.  That goes to one side of an LM311 comparator.
The lm311 switches a transistor that drives the fan.   It looks like
holding the sensor temp to +- 1/2 degree is easy.    Holding to only
0.5 C is not hard and might help.       Actually this controller is
going on a Rubidium oscillator, not an XO.   but if it works well I'll
build a few more.

 The idea is about the same is an ovenized XO but slightly more crude.
 Just aim the fan at the part you want to control and insulate the
sensor from airflow.     I'll know if this work in a few weeks


Chris Albertson
Redondo Beach, California


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