[time-nuts] ? phase comparison or other device

Pete peterawson at earthlink.net
Sun Jun 24 19:33:34 EDT 2007


This idea is NOT intended to rival the JPL results. Instead,
it's intended to be cheap, easy to replicate & allow rather
low cost instruments to be used to compare good sources
to parts in 1E12, quickly. The 1KHz heterodyne frequency
makes life much easier than 1Hz. Noisy components &
ground loops are still of concern, but not so hard to fix.

ADA4899-1 overload recovery is <50ns (per data sheet).

I've attached a rather poor schematic which doesn't show
power supply decoupling or the need to pull the disable 
pin high. The ADA4899-1 uses 14mA per part, but it's
quiet & fast. Metal film resistors are fine for this low
noise application & all are low values to keep noise down.

The inductors are easy to wind, but I found materials other
than moly permalloy powder to be too noisy. Even with
MPP material, cores with u>200 are prone to field induced
shifts which are unacceptable.

Pete Rawson
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