[time-nuts] FE-5680A tear down on Youtube

[Bob Smither]

Attila Kinali wrote:
> On Fri, 13 Jan 2012 12:50:19 -0500
> "Bob Camp" <lists at rtty.us> wrote:
> 
>> The gizmo on top of the crystal is a rapid transition thermistor. The
>> Russians came up with them for use in OCXO's back in the 1970's. It's there
>> to heat the VCXO crystal, sort of an OCXO.
> 
> Do you have any references to this? I couldn't find anything on the net.
> 
> 				Attila Kinali

>From http://wb9ipa.qrpradio.com/60meter/osc_filter/osc_filter.htm :

"PTC thermistors exhibit a unique behaviour, in that their resistance increases
as the temperature increases.  This temperature to resistance relationship is
very non-linear; in fact, the change becomes very rapid above a temperature
known as the Transition Temperature.  This property can be exploited to make a
very simple, self-regulating heater."

See also http://c-c-i.com/node/165 for an application note that has a pretty
good discussion of this.

-- 
Bob Smither, PhD                                   Circuit Concepts, Inc.
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   Friendly relations with all nations, entangling alliances with none.
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Smither at C-C-I.Com  http://www.C-C-I.Com  281-331-2744(office)  -4616(fax)
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