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Two single-channel fast-sequencing GPS receivers (of type K +K GPS5) tracking the GPS signals of all satellites in view and using carrier-phase smoothing have been studied in time-scale comparisons between the Physikalisch-Technische Bundesanstal (PTB) and the Technical University Graz (TUG). The receiver output signal is a IPPS pulse which is the physical representation of UTC(USNO) obtained as the average from the individual satellites (SATMIX). At PTB and TUG, the 1PPS is measured with respect to UTC(PTB) and UTC(TUG), respectively. After exchange of data, the time-scale differences UTC(PTB) - UTC(TUG) are calculated and compared with those obtained by the GPS common-view (CV) and TWSTT methods. These comparisons show that the daily mean values of UTC(PTB) - UTC(TUG) found with the SATMIX technique are by only a factor of 2 more noisy (about 4 ns) than those obtained with the CV and TWSTT methods (about 2 ns). Measurement results over about 1 year are presented. It appears that the SATMIX technique is an useful alternative method for time comparisons. An advanced version (K+K GPS5-2K) based on the same principle as the K+K GPS5 is under development. The expected features of the advanced receiver are described briefly., See also ADM001481. Presented at the Annual Precise Time and Time Interval (PTTI) Meeting (31st), held in Dana Point, CA on 7-9 December 1999. Published in the proceedings of the meeting, p383-392, 1999. Prepared in cooperation with Technical University Graz, Austria and Space Research Institute, Graz, Austria.

After a brief introduction and description of the portable station and a discussion of different approaches to use it for station calibration, the calibration trip is described and the results are presented. The calibrated TWSTFT measurements are compared with the GPS measurements calibrated by a GPS receiver trip carried out at the same time as the TWSTFT calibration and by previous GPS receiver trips. The findings are discussed and some envisaged activities using the portable station are mentioned., See also ADA415578. Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting(30th), held in Reston, VA, on 1-3 Dec 1998

Two-Way Satellite Time and Frequency Transfer (TWSTFT) is the most accurate and precise method of comparing two remote clocks or time scales. The accuracy obtained is dependent on the accuracy of the determination of the non-reciprocal delays of the transmit and the receive paths. When the same transonders in the satellite at the same frequencies are used, ten the non-receiprocity in the earth stations is the limiting factor for absolute time transfer., Presented at the Annual Precise Time and Time Interval Applications and Planning Meeting (27th) held in San Diego, CA on 29 November-1 December 1995. Published in the Proceedings of the Annual Procise Time and Time Interval Applications and Planning Meeting (27th), p359-372, 1995.

For a decade and a half GPS Common-View time transfer has greatly served the needs of primary timing laboratories for regular intercomparisons of remote atomic clocks. However, GPS as a one-way technique has natural limits and may not meet all challenges of the comparison of the coming new generations of atomic clocks. Two-Way Satellite Time and Frequency Transfer (TWSTFT) is a promising technique which may successfully complement GPS. For two years, regular TWSTFT's have been performed between eight laboratories situated in both Europe and North America, using INTELSAT satellites. This has enabled an extensive direct comparison to be made between these two high performance time-transfer methods. The performance of the TWSTFT and GPS Common-View methods are compared over a number of time-transfer links. These links use a variety of time-transfer hardware and atomic clocks and have baselines of substantially different lengths. The relative merits of the two time-transfer systems are discussed., Presented at the Annual Precise Time and Time Interval Applications and Planning Meeting (27th) held in San Diego, CA on 29 November-1 December 1995. Published in the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (27th), p347-358, 1995.

A fully automated two-way time and frequency transfer (TWSTFT) system including a satellite simulator, which allows to carry out signal delay measurements in conjunction with each time transfer measurement, is operated at the Technical University Graz (TUG). After a brief description of the system, results obtained during fifteen months of operation are presented and discussed. Finally envisaged experiments are mentioned., Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (27th) held in San Diego, CA on 29 Nov-1 Dec 1995. Published in the Annual Precise Time and Time Interval Applications and Planning, p303-311, Dec 1995.

The international transatlantic time and frequency transfer experiment was designed by participating laboratories and has been implemented during 1994 to test the international communications path involving a large number of transmitting stations. This paper will present empirically determined clock and time scale differences, time and frequency domain instabilities, and a representative power spectral density analysis. The experiments by the method of co-location which will allow absolute calibration of the participating laboratories have been performed. Absolute time differences and accuracy levels of this experiment will be assessed in the near future., Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (26th) held in Reston, VA on 6-8 December 1994. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (26th), p39-50, December 1994.

At the beginning of 1994, field trials for an international two-way time transfer experiment using the INTELSAT V-A(F13) satellite at 307oE were started. The experiment was set up to last one year and involved six European time laboratories and two North American time laboratories. Three times a week, 5-minute time transfer sessions were scheduled. At each of these laboratories, GPS common-view time observations were also performed. From September 22 to October 22, 1994 a calibration trip which visiting participating laboratories in Europe was organized. It involved a portable Vertex 1.8 meter two-way station (Fly Away STation[FAST]), belonging to USNO. and a portable GPS time transfer receiver, belonging to BIPM. The calibration trip was conducted by members of the staff of USNO and Observatoire de la Cote d'Azur (OCA). It provided differential delays of the satellite Earth stations and GPS receivers. The initial analysis of this calibration campaign are reported here., Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (26th) Held 6-8 Dec 1994 in Resotn, VA.

At the Technical University Graz (TVG), Austria, the Global Positioning System (GPS) has been used for time transfer purposes since the early 80's and from that time on local meteorological parameters are recorded together with each measurement (satellite track). The paper compares the tropospheric corrections (delays) obtained from models usually employed in GPS receivers and those using locally measured meteorological parameters., This article is from 'Proceedings of the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (25th) Held in Marina Del Rey, California on 29 November - 2 December 1993', AD-A280 955, p231-247.

For about one year the time scales UTC(OCA) and UTC(TUG) were compared by means of GPS and two-way satellite time transfer. At the end of the experiment both links were independently "calibrated" by measuring the differential delays of the GPS receivers and of the satellite earth stations by transportation of a GPS receiver and of one of the satellite terminals. The results obtained by both methods differ by about 3 ns, but reveal a seasonal variation of about 8 ns peak-to-peak which is likely the result of a temperature-dependence of the delays of the GPS receivers used. For the comparison of both methods the stabilities of the timescales are of great importance. Unfortunately during the last three months of the experiment a less stable clock had to be used for the generation of UTC(TUG)., See also ADA255837. Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (23rd) held in Pasadena, CA on 3-5 December 1991. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (23rd), p71-88, December 1991.

This very preliminary report briefly presents the first results on the time transfer experiments between TUG (Graz, Austria) and OCA (Grasse, France) using common view GPS, and two-way stations at both sites. The present data, providing a rms of the clock offsets of 2 to 3 nanoseconds for a three months period, have to be further analysed before any conclusions on the respective precision and accuracy of these techniques can be drawn. Two years after its start, the LASSO experiment is finally giving its first results at TUG and OCA. The first analysis of three common sessions permitted us to conclude that the LASSO package on board of Meteosat P2 is working satisfactorily, and that time transfer using this method should provide clock offsets at better than 1 nanosecond precision, and clock rates at better then 10(-12) s/s in a 5 to 10 minutes session. A new method for extracting this information from the raw data sent by LASSO should enhance the performances of this experiment, exploiting the stability of the on-board oscillator., See also ADA239372. Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (22nd) held in Vienna, VA on 4-6 December 1990. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (22nd), p575-582, December 1990.

Since 1980 time comparisons are carried out via OTS-2 between the Technical University Graz (Austria) and the Van Swinden Laboratory Delft (Netherlands). The method has been based on the use of the synchronization pulse in the TV-frame of the daily evening broadcasting of a French TV-programme to Northern Africa. Corrections, as consequence of changes in the position of the satellite coordinates are applied weekly after reception of satellite coordinates from ESOC. A description of the method is given as well as some of the particular techniques used in both the participating laboratories. Preliminary results are presented. Starting January 1982 the experiment will be supported by the EEC and enlarged by participation of NPL, PTB, DFVLR, LPTF and IEN., Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (13th), held in Washington, DC on 1-3 December 1981 and published in the proceedings of the same, p347-369. Prepared in cooperation with Technical Univ., Graz, Austria.

This report covers designing, building and testing of a variable speed fan drive. Speed control automatic from 0 to approximately 4900 rpm governed by engine coolant temperature. Unit includes a fail safe device which operates the fan at maximum speed in the event of a control failure. Unit also includes a deepwater fording switch to reduce fan speed when engine compartment is flooded. Direction of rotation is counter-clockwise viewed from output end. Tests performed on unit included a functional check on speed modulation, declutching, fail safe devices and deep water fording switch operation. All these tests were performed using a 1765 rpm electric motor. A high speed test of approximately 4800 rpm was also made to assure satisfactory operation at elevated speed. Results obtained from above tests indicate that fan drive will perform satisfactorily, but final evaluation is best obtained by operating under actual engine conditions.