Zaocheng Zhai

Miniature passive hydrogen maser at Shanghai Observatory

A miniature passive hydrogen maser is developed at Shanghai Observatory which employs compact cavity design and square wave frequency modulation. It is 704 mm high, 410 mm wide, 526 mm deep and weighs 40 kg. Preliminary measurements indicate a frequency stability of approximately /spl sigma/(2, /spl tau/)=1.0/spl times/10/sup -11/ /spl tau//sup -1/2/ (1s</spl tau/<5/spl times/10/sup 4/ s). Electrode-loaded resonant cavity and 4-pole state selector are used in passive hydrogen maser to reduce the size. Other design in the physical part is similar to the SOHM-III active hydrogen maser produced by Shanghai Observatory. Electronic part of the passive hydrogen maser comprises two frequency lock-loops: 10 MHz crystal oscillator frequency is locked to the hydrogen emission line and resonant cavity frequency is locked to the crystal oscillator frequency. Square wave frequency modulation is used in both loops in order to avoid the even harmonics in the sine wave modulation. At present, the initial test is finished. Next we will do some work to improve the performance of the miniature passive hydrogen maser.

The electronic improvement of the hydrogen maser for time keeping application

The hydrogen maser for time keeping must have excellent performances with long term frequency stability, low frequency drift and high reliability for long term working. Based on the research experiences on hydrogen masers of Shanghai Observatory, the key technical improvements for time keeping hydrogen masers are described in this paper. The mainly electronic improvements include: analysis on the principle of the cavity auto-tuning technique and improving the modulation system, the development of phase-lock receiver. The primary test result reaches the expert performance as follows: the frequency stability reaches 1.5E-15/day, frequency drift rate is 8.6E-16/day, and temperature sensitivity is 8.1E-15/°.

An experimental study for the compact hydrogen maser with a TE111 septum cavity

We have made experiments on our compact active hydrogen maser with the cylindrical TE111-mode septum cavity, which is almost one-half the conventional TE011-mode cavity in size. An inductive radiation signal was observed, but the maser did not produce self-oscillation. The system supports oscillation when the cavity is placed in an external feedback loop.

A transportable hydrogen maser for Australia Telescope

To equip the Chinese VLBI network, a transportable compact active hydrogen maser has been developed at Shanghai Observatory (SO) since 1985. So far five such masers have come into use for VLBI radioastronomy and some military. These hydrogen masers are all compact, relatively light, rugged and easily transportable. Including the electronics system, power supplies and stand-by batteries, their size is 57 cm/spl times/83 cm/spl times/127 cm and their mass is not more than 300 kg. In Nov. 1993, one of these masers was transported to Australia Telescope National Facility (ATNF) to determine its performance as a stable oscillator for VLBI. This paper describes the design and construction of the hydrogen maser and presents the results tested at Parkes Observatory of ATNF.