[time-nuts] Thunderbolt Power Supply Question
lists at rtty.us
Mon Apr 26 19:20:53 EDT 2010
In addition to the influence of the voltage on the oscillator, the voltage change also impacts the temperature control circuit. Most OCXO's control current through the heater rather than power in the heater. As you drop voltage, the power being controlled drops. The net effect is a change in control loop gain. A 10% change probably isn't going to massively degrade stability. A 2:1 change probably would be an issue.
On Apr 26, 2010, at 6:03 PM, Arthur Dent wrote:
> 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:
> "8-25. VOLTAGE REFERENCES (5.7V AND 6.4V)
> 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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