Attenuation measurement system in the frequency range of 10 to 100 MHz

An attenuation measurement system, which employs a traceable inductive voltage divider (IVD) at 1 kHz as a reference standard and dual-channel intermediate frequency (IF) substitution method, is developed as an attenuation standard in the frequency range of 10 to 100 MHz. High isolation between the channels is achieved by introducing an assembly of light emitting diode, optical fiber, and photodetector into the system. Sources of uncertainties of the system, such as leakage, are discussed and the expanded uncertainties are expected to be 0.001 dB for an attenuation range up to 20 dB and 0.04 dB for 80 dB.     

Primary calibration of hydrophones with extended frequency range 1 to 70 MHz using optical interferometry

A technique for the primary calibration of hydrophones based on an optical principle is presented. An interferometer determines the displacement of a pellicle mounted on the surface of the tank fluid perpendicular to the sound propagation axis; the known acoustic field is then measured using the hydrophone. The application range extends from 1 to 50 MHz and, with a lesser accuracy, to 70 MHz. The loaded and the open-circuit sensitivity are obtained pointwise, and the frequency and the number of the measurement points can be arbitrarily chosen. As an example, two membrane hydrophones with a spot diameter of 0.5 mm are calibrated, and the comparison with a theoretical model describing the acoustic and electrical properties of the hydrophone shows good agreement.     

Validation of RF power standard in the frequency range of 100 MHz to 18 GHz by an inter laboratory data comparison

Radio frequency (RF) power is one of the most important quantities in RF metrology. An inter laboratory data comparison of RF power for the validation of a coaxial microcalorimeter has been carried out between Physikalisch-Technische Bundesanstalt (PTB-Germany) and National Physical Laboratory India (NPLI). A coaxial thermistor mount equipped with type N connector is used for this intercomparison. The results show good agreement in measuring the effective efficiency of the coaxial thermistor mount between the two laboratories within their claimed expanded uncertainty. It confirms the equivalence of national standards for RF power in the frequency range of 100 MHz to 18 GHz.     

Investigation of a power divider using a coaxial probe array in a coaxial waveguide

A novel coaxial-waveguide power divider using coaxial probe array that achieved low-loss probe-to-waveguide transitions is presented. The small reflection theory of transverse electomagnetic (TEM) lines is extended to synthesise the gradual waveguide taper, and the equivalent-circuit approach is applied to analyse the coaxial probe array. The design and simulation of a single probe-to-waveguide transition have been developed. The detailed design, simulation, fabrication and measurements of a four-way coaxial power divider are discussed. The measured results agree well with the simulated results. The measured 15 dB return loss bandwidth of this waveguide power divider is demonstrated to be 8.2 GHz (fL = 7.8 GHz, fH = 16 GHz) and its 0.5 dB insertion loss bandwidth 11 GHz.     

A novel method for determining calibration and behavior of PVDF ultrasonic hydrophone probes in the frequency range up to 100 MHz

A new calibration technique for PVDF ultrasonic hydrophone probes is described. Current implementation of the technique allows determination of hydrophone frequency response between 2 and 100 MHz and is based on the comparison of theoretically predicted and experimentally determined pressure-time waveforms produced by a focused, circular source. The simulation model was derived from the time domain algorithm that solves the non linear KZK (Khokhlov-Zabolotskaya-Kuznetsov) equation describing acoustic wave propagation. The calibration technique data were experimentally verified using independent calibration procedures in the frequency range from 2 to 40 MHz using a combined time delay spectrometry and reciprocity approach or calibration data provided by the National Physical Laboratory (NPL), UK. The results of verification indicated good agreement between the results obtained using KZK and the above-mentioned independent calibration techniques from 2 to 40 MHz, with the maximum discrepancy of 18% at 30 MHz. The frequency responses obtained using different hydrophone designs, including several membrane and needle probes, are presented, and it is shown that the technique developed provides a desirable tool for independent verification of primary calibration techniques such as those based on optical interferometry. Fundamental limitations of the presented calibration method are also examined.     

Accurate measurement of power system frequency using a digitalsignal processing technique

This paper describes the design, computational aspects, and implementation of a digital signal processing technique for measuring the operating frequency of a power system. The technique provides correct and noise-free estimates for near-nominal, nominal, and off-nominal frequencies in about 25 ms, and it requires modest computations. The proposed technique is implemented using a DSP-based board and has been extensively tested using voltage signals obtained from a dynamic frequency source and from a power system. Some test results are presented in the paper     

International comparison GT-RF 75 A 11: RF power at 12 GHz, 14 GHzand 17 GHz in 50 Ω coaxial line

This paper deals with the results of an international comparison measurement of the effective efficiency E of commercial 50 Ω/7 mm coaxial thermistor RF power standards fitted with PC-7 precision connectors. The measurement frequencies were 12 GHz, 14 GHz and 17 GHz. The national laboratories of metrology of eight countries (Australia, Canada, France, Hungary, Italy, the Netherlands, USA and Germany) participated in this comparison which was organized by the Radio Frequency Working Group of the Comite Consultatif d'Electricite (CCE). The Physikalisch-Technische Bundesanstalt (PTB, Germany) acted as the pilot laboratory. The standards showed only a small linear negative drift in E, as found by linear regression analysis. For most of the mean values of E reported by the laboratories, the deviations from the regression values were small (not larger than 0.004); only in two cases were the deviations 0.006 and 0.0085     

A tower structured scintillator-lead photon calorimeter using a novel fiber optics readout system

Described is the construction and the performance of a tower-structured scintillator-lead photon calorimeter using a novel fiber optics readout system. The calorimeter is divided into 9 individual towers. Each tower has a cross section of 5 × 5 cm² and consists of 60 layers of 2 mm lead plus 5 mm thick scintillator. The four sides of each tower are covered by thin acrylic sheets (1.5 mm thick) doped with a wavelength shifting material. The light produced in each scintillator plate is first converted in these sheets, then converted a second time in a set of polystyrene optical fibers (diameter 2 mm) which run longitudinally through the calorimeter along the corners of each tower. A small diameter photomultiplier was attached to the fibers at the back end of the calorimeter. The obtained energy resolution with incident electrons in the range of is . The uniformity of response across the front face of each tower was measured.     

Global behaviour of power system frequency in korean power system for the application of frequency monitoring network

Since the concept of building an Internet-based real-time Global Positioning System synchronised wide-area frequency monitoring network (FNET) was proposed in 2001, FNET has been implemented in the Power IT Laboratory at Virginia Polytechnic Institute and State University (Virginia Tech.), and now it is used in monitoring the power system frequency in continuous time at more than 40 locations in the United States. A global view of the power system frequency based on FNET measurements helps understand the frequency behaviour more correctly, and its various applications such as event location estimation have been also studied. The global behaviour of power system frequency in the Korean power system, which has very unique characteristics, is analysed and thereby the possibility of applying FNET is studied. Although the scale of the Korean power system is much smaller than the US power systems, its global behaviour of frequency has its own characteristics, and those findings will help us understand any correlation between system characteristics and the global frequency behaviour. What is found here could serve as the first step to the application of FNET to the Korean power system.     

Towards accurate measurement of the frequency dependence of capacitance and resistance standards up to 10 MHz

Progress toward an understanding of the frequency dependence of capacitance and resistance standards at frequencies up to 10 MHz is presented. A qualitative comparison is also made for capacitance and dissipation factor measurements between the National Physical Laboratory (NPL) high-frequency four terminal-pair (4TP) bridge and a commercial impedance analyzer for the first time. A set of novel high-frequency calculable coaxial resistance standards, of nominal 100 /spl Omega/ and 1 k/spl Omega/ values, have been developed and their calculated frequency dependence up to 1 MHz is given.     

真空比对法校准装置的研究

真空比对法校准装置采用了动态直接比对法、静态直接比对法和静态膨胀法,在一台装置上复合了三种方法,满足了拓宽量程的需求.该装置可以1×105-5×10-4 Pa范围内的各类真空规进行校准,是一种结构简单、操作方便、检定效率高、实用性强的真空标准装置.整套装置由涡轮分子泵、校准容器、副标准真空计和金属膨胀阀等部件组成,主要技术指标符合国际标准化组织和国内有关真空标准的规定.     

Measurement techniques and results of an intercomparison for RFpower in a 3.5 mm coaxial line up to 26 GHz

The methods and results of an international comparison are presented for measurements of RF power in a 3.5 mm coaxial line at seven frequencies up to 26 GHz. Three national laboratories of metrology having different measurement techniques participated in the comparison. The agreement between the mean values of the calibration factor of the traveling standard reported by the participants is well within their reported uncertainties (k=2), which are between 0.5% and 3.1%     

Measurement of the instantaneous frequency of broadband signals in a short observation interval

A high-speed method of estimating the instantaneous frequency of broadband signals with slowly varying amplitude and phase using a short sample in real time is proposed, and results of numerical modeling of the measurement procedure are presented. The speed of response and noise immunity of the method is compared with the existing method, based on the theory of signal “splitting.” It is shown that in both methods it is possible to use recurrence relations, which considerably reduce the measurement time. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 50–54, February, 2008.     

Analysis of the global reduction of broadband noise in a telephone kiosk using a MIMO modal ANC system

The possibility of implementation of ANC system for global reduction of broadband noise in a telephone kiosk application has been studied in this paper. By using a modal model of the acoustic environment of the enclosure the shape modes and their frequencies are obtained and suitable bandwidth for the controller design is calculated. Analysis shows that because of existing of some degenerate modes in this application, the control action is complicated. Simulation results show that how positions and number of loudspeakers and microphones will change the performance of the controller and its corresponding control effort. Based on these results and analysis a reasonable size for the controller and proper locations for sensors and actuators are proposed. Simulation results also show the effectiveness of the proposed system in reduction of the acoustic potential energy in the kiosk.