Characteristics of the Nasa Research Hydrogen Maser

Abstract

The Johns Hopkins University, Applied Physics Laboratory, under contract to NASA/Goddard Space Flight Center, has engineered a new generation of field operable hydrogen masers (NR) based on prior NASA NP and NX designs. These units incorporate improvement in magnetic shielding, lower noise electronics, better thermal control and have a microprocessor built into the instrument for operation, monitoring and diagnostic functions. The microprocessor data and control is remotely accessible over telephone links. The masers are ruggedly built for transportability and ease of service anywhere in the world.

The frequency is settable over a range of ±5 × 10^-8 to a resolution of 7 parts in 10¹⁷ without losing coherent phase; the time can be set to a resolution of better than 5 picoseconds. A flicker floor of 1 part in 10¹⁵ has been obtained at 2000 seconds under favourable environmental conditions. The DC magnetic shielding factor is greater than 18,000. The thermal co-efficient of frequency is less than 5 × 10^-14/°C. A line Q of approximately 2 × 10⁹ is realized at low flux levels. The jitter on 5 MHz is approximately 0.3 ps rms. Four 5-MHz output signals are isolated by 120 dB from both the internal control loops and between outputs. An internal clock with internal standby power provides one pulse per second on two separate terminals stepwise adjustable in 200 ns steps or continuously adjustable by timed frequency offsets.