Environmental effects in frequency synthesizers for passive frequency standards

This paper reviews the environmental effects in synthesizers designed to support a frequency stability of 10^-13 τ^-1/2 in short term and 10^-17 in the long term. Specifically we consider the effects of temperature, pulling by spurious spectral lines, vibration effects, and pickup of spurious rf signals. We show that the temperature coefficient of the new NIST HR1 synthesizers is less than 1 ps/K and that the pulling from spectral purity is less than 3×10^-20 in NIST-7, our primary thermal cesium beam standard. The pulling for slow cesium standards should be lower. We also show that the pulling due to spurious lines in Ramsey standards with narrow line widths can be manipulated to examine spectral pulling. The fractional frequency stability is better than 3×10^-14 τ^-1/2 for measurement times out to 10⁴ s and reaches 10^-16 in about 15 minutes in a standard laboratory environment of roughly +/-0.5 K without the need of additional thermal regulation