[time-nuts] Thunderbolt Power Supply Question

Arthur Dent golgarfrincham at yahoo.com
Mon Apr 26 18:03:04 EDT 2010

Ed Palmer-"Every oscillator has a spec for frequency shift due to power supply variation,
but maybe you'd see a big change when you lost regulation.  Have to think about that."

I have done this a few times with oscillators that contain internal regulators and the output
level remains constant and the frequency display on my scope (triggered by a standard)
remains stable until you reach the point where the internal regulator output starts to drop
and you do see a significant change. Because the oscillator and buffer stages generally
only draw a few ma., a low power linear regulator with good filtering is easy to design.

HP says this about the simple circuit they used in the 10811:
 8-26. Constant current diode CR2 feeds 1 mA to zener diode CR3 providing 6.4Vdc for the
 EFC varactor reference. R12 and C15 form a filter to attenuate noise from the zener

As to the -12VDC supply, one unit that used the Thunderbolt used -7VDC instead of 
-12VDC and the same Thunderbolt works just fine with either voltage.


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