[time-nuts] Improving the stability of crystal oscillators

Rick Karlquist richard at karlquist.com
Thu Oct 11 17:55:38 EDT 2007

We went through this tradeoff on the E1938A.  Resistive heaters
can be distributed.  However, it is very inefficient to drive
them with transistors, because then you waste a lot of power
heating the transistors, which is waste heat if resistive heating
is used.  Prior to the 10544, they just put up with this.  The
10544 used a switching regulator for up the efficiency, but it
put a 1 kHz spur on the oscillator.  The 10811 used two transistors
on opposite sides to try to sort of distribute the heat.  On
the E1938A, we looked at an array of small surface mount transistors
to have the best of both worlds.  However, this turned out not to
be manufacturable and we settled for resistive heaters (back to

Rick Karlquist N6RK

Bruce Griffiths wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+richard=karlquist.com at febo.com RETRY
> Neville Michie wrote:
>> If you use a transistor as a heater, the full supply voltage is
>> across the
>> element all the time, so heating is proportional to the current flowing.
>> Neville
> Neville
> However using a transistor has the disadvantage of a small area heat
> source rather than the large area heat source possible with a heater
> winding.
> Using a small area heat source produces significant temperature gradients.
> Bruce
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