A direct conversion transmitter comprising two local oscillators, an in-phase and quadrature modulating signal and in-phase and quadrature modulators, adds a leakage detector and corrective algorithm with one or more digital to analog converters to generate a corrective signal. The corrective signal corrects for, minimizes, and suppresses local oscillator carrier leakage into the transmitted signal. In accordance with the invention, direct up transmitter carrier leakage is automatically measured at regular intervals during the transmit cycle. A DC correction, or a correction waveform as a function of time, is input to both the “in-phase” and “quadrature” modulators at the baseband input. The two correction signals are tuned according to a minimization algorithm to achieve the lowest possible carrier component in the spectral output of the transmitter at its ambient operating conditions and present power output level. As the ambient conditions, such as temperature, and transmitter power level changes, the two correcting input DC currents, or correction waveforms, are further tuned towards the optimal values for that operating condition. Optimization is accomplished by an adaptive feedback technique employed to achieve maximum carrier suppression.

Method and apparatus for suppressing local oscillator leakage in a wireless transmitter

The discovery of the Josephson effects 50 years ago initiated a revolution for electrical voltage metrology. This revolution started with single Josephson junctions delivering a few millivolt at most. Meanwhile, highly integrated series arrays containing more than 10 000 or even 300 000 junctions have been developed and fabricated for output voltages up to 10 V. Josephson voltage standards are nowadays used in many laboratories worldwide for dc applications. After their adoption for the representation of the unit of voltage in 1990, the focus of research shifted towards programmable Josephson series arrays. The increasing interest in highly precise ac voltages resulted in new developments for their metrological applications in the last 15 years. This paper summarizes the principal contributions from PTB to the present state of Josephson voltage standards with particular focus on developments and applications for ac standards in metrology and our proof-of-concept demonstrations. The presentation includes the two most promising versions of ac standards, being the programmable Josephson voltage standard based on binary divided series arrays and the Josephson arbitrary waveform synthesizer based on a pulse-driven series array.

https://iopscience.iop.org/article/10.1088/0957-0233/23/12/124002/pdf

Development and metrological applications of Josephson arrays at PTB

A high-accuracy system for calibration of electronic instrument transformers with digital output is described. Its design is based on International Electrotechnical Commission (IEC) standards 61850, 60044-8, and 60044-7. The performance of the calibration system has been evaluated. Its estimated relative uncertainty (2/spl sigma/) is within 40/spl middot/10/sup -6/ in magnitude and within 40 /spl mu/rad in phase.

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Calibration system for electronic instrument transformers with digital output

This paper describes an outdoor calibration of an instrument current transformer connected to 400 kV transmission line. The method of generation of the high current and the accuracy of calibration are discussed. The reference current measuring system consists of a current shunt, a Rogowski coil, two digitizing voltmeters and a computer to control voltmeters. The Rogowski coil is calibrated on-site with the current shunt. The output voltage of the Rogowski coil is not integrated, but it is scaled according to the on-site calibration result. Estimated uncertainties for ratio and phase displacement are less than 0,01% and 100 murad, respectively.

On-site calibration of a current transformer using a Rogowski coil

We present the results of an analytical study aimed at characterizing the critical parameters affecting the mutual inductance M between Rogowski coils and primary conductors. The analysis is based on the method of the mutual partial inductances and it is applied to various case studies. Calculations are carried out for Rogowski coils having a few turns, hundreds, and even thousands of turns with uniform and nonuniform windings. We also provide the results of an experimental analysis performed on a Rogowski coil with a small number of turns for comparison with the proposed technique.

Critical parameters for mutual inductance between Rogowski coil and primary conductor

Measurement of the phase angle between fundamental components of distorted periodic signals at power frequencies is described. It is based on a nonsynchronous multirate digital filtering algorithm, which is applied to the voltage and/or current signals to be measured. The digital filters implemented are designed to suppress the higher harmonics and ensure the accuracy of measurement. The measurement method is insensitive to frequency variations in a wide frequency band around the nominal frequency. For a frequency band of /spl plusmn/10% around the nominal frequency, this method can resolve phase differences of less than 5 /spl mu/rad with an uncertainty of less than /spl plusmn/25 /spl mu/rad.

Phase measurement of distorted periodic signals based on nonsynchronous digital filtering

A new high-accuracy system for power-frequency calibration of Rogowski coils is described in this paper. The calibration system is based on nonsynchronous digital sampling. An automated prototype of the calibration system operates at currents of up to 2000 A. A semiautomated system is capable of operating at currents of up to 60 000 A. The best uncertainty (k = 2) of the calibration system is estimated to be better than 50 muA/A for magnitude and 50 murad for phase.

Calibration of Rogowski coils at power frequencies using digital sampling

A new system for calibration of Rogowski coils at frequencies up to 10 kHz, based on a reference current transformer, a reference ac shunt, and a digital sampling system, is described in the paper. The calibration system has been automated, and its performance has been evaluated. At the frequency of 10 kHz, the calibration system is capable of generating currents up to 100 A. At power frequencies, it is capable of generating currents up to 2000 A. The best uncertainties (k = 2) of the calibration system are estimated to be less than 500 ?A/A for magnitude and 500 ?rad for phase at 10 kHz and an order of magnitude better at power frequencies.

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Calibration of Rogowski coils at frequencies up to 10 kHz using digital sampling

The development of a high-voltage (HV) current measurement system for on-site/in-situ calibrations in power systems is described in the paper. The system is based on an optically isolated hybrid two-stage current transformer with electronic circuitry that performs A/D conversion. It uses a fiber optic link for data transmission to a ground station and a laser-driven fiber optic link for supplying power to the electronic circuitry of the remote module at HV. The uncertainty of the current-ratio measurement is estimated to be less than 100middot10-6 both in-phase and quadrature

Branislav Djokic

Papers

Calibration system for electronic instrument transformers with digital output

Phase measurement of distorted periodic signals based on nonsynchronous digital filtering

Calibration of Rogowski coils at power frequencies using digital sampling

Calibration of Rogowski coils at frequencies up to 10 kHz using digital sampling

An optically isolated hybrid two-stage current transformer for measurements at high voltage