Optimization of passive hydrogen standard frequency instability

Abstract

Summary form only given. The frequency instability of the passive hydrogen standard due to quantum hydrogen discriminator, receiver thermal noises and crystal oscillator phase fluctuations near frequency modulation harmonics of hydrogen maser interrogation signal is analyzed. The passive hydrogen standard block-diagram with single phase modulation interrogation signal of quantum hydrogen discriminator is considered for the condition that phase modulation frequency /spl Omega//sub m/ is much more than hydrogen spectral line halfwidth /spl gamma/. This standard has two automatic frequency control loops: for crystal oscillator and for microwave cavity. New dependences of frequency instability via interrogation signal parameters are defined. The frequency instability minimum for the passive hydrogen standard is at phase modulation index m=2.0-2.2, saturation parameter S/sub 0/=0.3-1.0 and is defined generally by noise in the automatic frequency control loop of the crystal oscillator. The dependence of the hydrogen passive standard frequency instability via interrogation signal modulation frequency is weak for 0.2/spl beta/</spl Omega//sub m/<0.5/spl beta/, where /spl beta/ is halfwidth band of cavity. It is shown that the crystal oscillator phase fluctuations on even harmonics of modulation frequency have an influence on passive hydrogen standard frequency instability.