Bruce, 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 showpower 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. Regards, Pete Rawson
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