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Comparisons are made between the NP series and the NX series of hydrogen masers. A field operable hydrogen maser (NR series) is also described. Atomic hydrogen primary frequency standards are in development stages. Standards are being developed for a hydrogen beam frequency standard and for a concertina hydrogen maser.
The note reports results of an unsuccessful search for the four hyperfine transitions in the cited rotational state of interstellar CH, which was performed using a 25.6-m radio telescope equipped with a traveling-wave maser radiometer. The frequency interval covered ranged from 4677 to 4850 MHz; the sources observed were W3 Cont, W51, Orion A, and IRC+10216. It is shown that the lines in the present excited state cannot be expected to be observed if the state is populated according to thermodynamic equilibrium at the kinetic temperature of the medium. The possibility is considered of detecting thermally excited CH in a more compact region and of detecting excited-state CH maser lines. It is concluded that no strong CH maser lines exist for the frequencies and sources covered.
The combination of a cryogenically-cooled parametric upconverter and a higher frequency maser post amplifier was proposed as a method of achieving maser-like receiver noise temperatures over much larger instantaneous bandwidths and tuning ranges than are presently obtainable with masers in the range of 1 to 18 GHz. An experimental 2.0- to 2.5-GHz parametric upconverter/maser system was developed to explore these possibilities. Initial tests of this system resulted in an effective input noise temperature of 3.1 K at 2295 MHz and 3.2 K at 2388 MHz. The parametric upconverter logged over 1500 hours at 4.5 K and underwent 5 thermal cycles (300 K to 4.5 K to 300 K) without degradation.
A Scout D rocket was launched from Wallops Island, Virginia, carrying an atomic hydrogen maser oscillator system as the payload. The frequency of signals from the oscillator was monitored on the ground at Merritt Island, Florida, by using two hydrogen masers as comparison oscillators. The first-order Doppler shift in the signals was eliminated by a go-return transponder link to the payload, and the resulting data, representing the relativistic shifts, were recovered and recorded. The objective was to measure directly the effect of gravitational potential on the frequency of an atomic hydrogen maser assuming it to be a 'proper' clock. A gravitational effect amounting to some 4.5 parts in 10 to the 10th power was measured with an oscillator having a stability better than 1 part in 10 to the 14th power. Therefore, to make the best possible use of the oscillator, all frequency shifts at the 2 to 5 X 10 to the -15 power level in delta f/f in the system must be accounted for. This includes all the phase variations that can cause such a shift to appear. The experiment, the data available and the manner in which they were processed, and the results are described.
A K-band reflected-wave ruby maser was used on the 64-meter (DSS-43) antenna at the Tidbinbilla Tracking Station, near Canberra, Australia. Spectral line observations were carried out near 22 GHz for water vapor sources and near 24 GHz for ammonia sources. The water vapor observations were made in the direction of known southern OH and H2O maser sources. All of the previously detected water line sources examined were detected. In addition, two new water vapor maser sources were discovered, G301.1+1.1and G308.9+0.1. The spectrum of G301.0+1.1 is presented six ammonia sources were found: G291.3-0.7, G305.4+0.2, G322.2+0.6, G327.3-0.5, G333.6-0.2, and G268.4-0.8. Spectra of two of these sources, G291.3-0.7 (RCW 57) and G305.4+0.2, are presented. Both show clearly the presence of the quadrupole splitting satellite lines that will allow the determination of NH3 optical depths in these clouds.
The increased bandwidth and sensitivity of the DSN maser-based receiver systems along with the increase in worldwide microwave spectrum usage dictated the need for employing additional measures to protect these systems from RFI (radio frequency inerference). Both in-band and out-of-band microwave signals at the input of the Deep Space Network (DSN) traveling wave masers (TWM) can adversely affect the maser performance in a variety of ways. Filters fabricated from superconducting materials operating below their superconducting transition temperature (Tc) possess the most potential for providing the necessary RFI protection without degrading the system performance.
Application of a dc magnetic field on an RF hydrogen gas dissociator led to the development of a more efficient source of atoms for hydrogen masers. The influence of the applied magnetic field on the plasma and some details of the resulting enhancement of the dissociation efficiency are discussed. Ways that this improved efficiency can result in the enhancement of the operation and field life of hydrogen masers, as well as aid the development of spaceborne masers, are considered.
Extremely low noise, high performance, wideband buffer amplifiers and buffered phase comparators were developed. These buffer amplifiers are designed to distribute reference frequencies from 30 KHz to 45 MHz from a hydrogen maser without degrading the hydrogen maser's performance. The buffered phase comparators are designed to intercompare the phase of state of the art hydrogen masers without adding any significant measurement system noise. These devices have a 27 femtosecond phase stability floor and are stable to better than one picosecond for long periods of time. Their temperature coefficient is less than one picosecond per degree C, and they have shown virtually no voltage coefficients.
The concept of placing a hydrogen maser high stability clock in Earth orbit to provide accurate time and frequency comparisons worldwide to major timing centers and to a large number of radio observatory antenna sites involved in VLBI measurements was studied. The proposal was chiefly directed toward studies and initial hardware designs for time comparisons between hydrogen maser frequency standards and to modifications of the hydrogen maser for long-term use in space.
A superconducting comb structure as a slow-wave element in a traveling-wave maser will significantly improve maser noise temperature and gain by reducing the insertion loss. The results of the insertion loss measurements of superconducting niobium slow-wave structures subjected to maser operating conditions at X-Band frequencies are presented.
The application of a sensitive hydrogen gas detector led to the observation of a significant increase in the efficiency of atom production of a magnetically enhanced dissociator. An increase of about 7000% in the production of atoms in the hyperfine state desired for maser operation is observed at certain values of the applied magnetic field. A preliminary test of the dissociator in the maser led to an observed increase of 6.18 dB in the maser power.
Understanding the dynamical structure of circumstellar envelopes around cool giant and supergiant stars depends critically on the knowledge of what happens in the 'near zone' of the envelope, within a few stellar radii of the star. One probe with adequate angular resolution to study the near zone is VLBI observation of the SiO masers. It is shown that VLBI maps of VX Sgr establish that the particle density in the SiO masers is very high (about 10 to the 12th/cu cm), indicating that the masers form in dense cloudlets and not in a spherically expanding wind. The implications of these results for the mechanism of mass loss are discussed.
Maser emission from OH and H2O is observed to be present over an exceptionally wide range of velocities in the cold, stellar infrared source IRAS 16342-3814. OH emission at 1612, 1665, and 1667 MHz spans 130 km/s, a range far larger than in any other known OH/IR star. The H2O emission features appear as two widely separated doublets with a full velocity spread of 259 km/s. Several lines of evidence point to the conclusion that IRAS 16342-3814 is an evolved star with a bipolar outflow, related to objects such as OH 231.8 + 4.2 and M1 - 92. The H2O masers are interpreted as streams or clumps of molecular gas forced out the polar axes by, or as part of, a wind from an accretion disk, while the OH masers appear to arise from lower velocity material at intermediate latitudes.
The two-dimensional particle simulations and three-dimensional ray-tracing calculations presently used to characterize the generation and propagation of EM radiation due to the auroral plasma cavity's electron cyclotron maser instability incorporate a continuous flow of primary energetic electrons along the magnetic field. The magnetic field gradient is found to be unimportant in accounting for various quasi-local properties of the maser instability. The maser instability can produce the observed amplification of auroral kilometric radiation above cosmic background levels within a distance smaller than the dimensions of the auroral cavity.
Observations are presented of the H II region complex in W51 made with a mm interferometer. W51 is a region of massive star formation approx. 7 kpc distant from the sun. This region has been well studied in both the IR and submillimeter, the radio, as well as the maser transitions. These previous observations have revealed three regions of interest: (1) W51MAIN, a know of bright maser emission near two compact H II regions W51e1 and W51e2 (W51MAIN is also the peak of the 400 micron emission indicating that the bulk of the mass is centered there; (2) W51IRS1 is a long curving structure seen at 20 micron and at 2 and 6 cm but not at 400 micron; (3) W51IRS2 (also known as W51NORTH) is another compact H II region slightly offset from an 8 and a 20 micron peak and a collection of masers. Some conclusions are as follows: (1) SO and H(13)CN emission are similar and coincide with outflow activity; (2) HCO+ spectra show evidence for overall collapse of the W51 cloud toward W51MAIN; (3) A previously undetected continuum peak, W51DUST, coincides with the molecular peak H(13)CN-4; and (4) Dust emission at 3.4 mm reveals that about half of the 400 micron emission comes from the ultracompact H II region e2, and the rest from W51e1 and W51DUST.
Some aspects of research development and production of quantum frequency standards, carried out in QUARTZ Research and Production Association (RPA), Gorky, U.S.S.R., were investigated for the last 25 to 30 years. During this period a number of rubidium and hydrogen frequency standards, based on the active maser, were developed and put into production. The first industrial model of a passive hydrogen maser was designed in the last years. Besides frequency standards for a wide application range, RPA QUARTZ investigates metrological frequency standards--cesium standards with cavity length 1.9 m and hydrogen masers with a flexible storage bulb.
A model for AKR frequency fine structure in which the fine structure is a natural consequence of the emission of electron cyclotron maser radiation in a nonuniform magnetic field is presented. The model is examined by using 1D electromagnetic particle-in-cell simulations. It is found that maser radiation is emitted as individual wave packets combine to form the drifting emission features that make up the fine structure. Rising frequency drifts are associated with wave packets emitted independently of one another. Wave packets that interact with one another produce features with falling frequency drift. The emission features produced have a large spread in both positive and negative frequency drift rates. The average positive drift rate of rapidly drifting features is found to be approximately proportional to the maser growth rate.
An experiment was conducted to investigate the equivalence of two methods of time transfer in a noninertial reference frame: by means of an electromagnetic signal using laser light pulses and by means of the slow ground transport of a hydrogen maser atomic clock. The experiment may also be interpreted as an investigation of whether the one-way speeds of light in the east-west and west-east directions on the rotating earth are the same. The light pulses were sent from a laser coupled to a telescope at the NASA Goddard Optical Research Facility (GORF) in Greenbelt, Maryland to the U.S. Naval Observatory (USNO) in Washington, DC. The optical path was made possible by a 30-cm flat mirror on a water tower near GORF and a 25-cm flat mirror on top of the Washington National Cathedral near USNO. The path length was 26.0 km with an east-west component of 20.7 km. The pulses were reflected back over the same path by a portable array of corner cube reflectors. The transmission and return times were measured with a stationary Sigma Tau hydrogen maser and a University of Maryland event timer at GORF, while the times of reflection were measured with a similar maser and event timer combination carefully transported to USNO. Both timekeeping systems were housed in highly insulated enclosures and were maintained at constant temperatures to within +/- 0.1 C by microprocessor controllers. The portable system was also protected from shock and vibration by pneumatic supports. The difference delta(T) between the directly measured time of reflection according to the portable clock and the time of reflection calculated from the light pulse signal times measured by the stationary clock was determined. For a typical trip delta(T) is less than 100 ps and the corresponding limit on an anisotropy of the one-way speed of light is delta(c/c) is less than 1.5 x 10(exp -6). This the only experiment to date in which two atomic clocks were calibrated at one location, one was slowly transported to the other end of a path, and the times of transmission, reflection, and return of short light pulses sent in different directions along the path were registered.