VHF and UHF Attenuation Measurements to 140 dB

A system has been assembled for rapid comparison of production step attenuators, with a reference attenuator using direct substitution at spot frequencies in the VHF and UHF range. The total attenuation range for such tests is 140 dB, with a basic resolution of ±0.01 dB and with maximum errors of ±0.08 dB, attributable, primarily, to reflection inaccuracies. Simplified methods for measurement to 110 dB at any selected frequency are described, as well as additional refinements permitting spot frequency measurements to 170 dB. The basic equipment required for these measurements is a well-shielded signal source generating in excess of 100 mW, and a low-noise narrow-band receiver with provision for locking the signal frequency to the center of the receiver passband.     

Residual phase noise measurements of VHF, UHF, and microwavecomponents

The results of residual phase noise measurements on a number of VHF, UHF, and microwave amplifiers, both silicon (Si) bipolar junction transistor (BJT) and gallium arsenide (GaAs) field effect transistor (FET) based, electronic phase shifters, frequency dividers and multipliers, etc., which are commonly used in a wide variety of frequency source and synthesizer applications are presented. The measurement technique has also been used to evaluate feedback oscillator components, such as the loop and buffer amplifiers, which can play important roles in determining an oscillator's output phase noise spectrum (often in very subtle ways). While some information has previously been published related to component residual phase noise properties, it generally focused on the flicker noise levels of the devices under test, for carrier offset frequencies less than 10 kHz. The work reported herein makes use of an extremely low noise, 500 MHz surface acoustic wave resonator oscillator (SAWRO) test source for residual phase noise measurements, both close-to-and far-from-the-carrier. Using this SAWRO-based test source at 500 MHz, we have been able to achieve a measurement system phase noise floor of -184 dBc/Hz, or better, for carrier offset frequencies greater than 10 kHz, and a system flicker phase noise floor of -150 dBc/Hz, or better, at 1 Hz carrier offset. The paper discusses the results of detailed residual phase noise measurements performed on a number of components using this overall system configuration. Several interesting observations related to the residual phase noise properties of moderate to high power RF amplifiers, i.e., amplifiers with 1 dB gain compression points in the range of +20 to +33 dBm, are highlighted     

In situ occupational and general public exposure to VHF/UHF transmission for air traffic communication

Occupational and general public exposure due to very high frequency (VHF)/ultra high frequency (UHF) transmission centres for verbal communication for air traffic control is investigated in situ for the first time. These systems are used for communication with aircraft, resulting in different human exposure from that of classical broadcasting. Measurement methods are proposed for the exposure assessment, and a measurement campaign is executed in three transmission centres. By investigating the temporal behaviour of the VHF signals for 6 d, a realistic worst-case duty cycle of 29 % is determined. Periods of high exposures corresponding with high aircraft traffic are from 7 a.m. to 1 p.m. and in the evening. All measured electric-field values satisfy the International Commission on Non-ionizing Radiation Protection guidelines. Fields vary from 0.2 to 21.1 V m(-1) for occupational exposure and from 0.007 to 8.0 V m(-1) for general public exposure. The average fields equal 5.2 V m(-1) for workers, and 0.7 V m(-1) for general public.     

Recent Advances in Broad-Band VHF and UHF Transmission Line Methods for Moisture Content and Dielectric Constant Measurement

Recent advances in VHF and UHF transmission line methods for determining either the complex permittivity or moisture content of bulky or film-like materials, or the thickness of film-like materials are discussed. These methods include TDR, CW phase, and |S21| transmission methods and employ a time-domain reflectometer (TDR), a vector voltmeter, and a network analyzer, respectively. Each technique involves monitoring the change of the transmission line parameters of a balanced open line, or of an unbalanced coaxial transmission line, when loaded with the material under test. Particular attention is given to the frequency range 10 to 1000 MHz and to broad-band methods. Experimental results are presented for several common materials, viz. concrete, asphalt, Plexiglas, moist paper, and moist soil.     

Design of high-Q UHF radio-frequency identification tag antennas for an increased read range

In order to increase the radio-frequency identification (RFID) operation distance, read range analysis was performed based on a simple equivalent circuit of the ultra high frequency (UHF)-band passive RFID tag. The analysis shows that a tag with a large Q-factor leads to an increased input voltage in the tag chip and thus enhances the efficiency. Based on this analysis, a compact (37.5 mm 44 mm) RFID antenna employing inductive coupling between the radiation and feeding portions was designed. Simple adjustments of the two structural parameters of the antenna allowed for easy control of the antenna resistance and inductive reactance, from which a high Q-factor requirement could be readily satisfied. For a conjugate match to the tag chip impedance of 11-j127 Omega, a Q-factor of 11.5 was achieved. The designed RFID tag has a 3 dB radar cross-section (RCS) bandwidth of 6.5 , which is wide enough to handle the impedance detuning caused by the material properties of the attached objects. The designed RFID tag antenna was fabricated and a reading range test in an anechoic chamber was performed using two methods. When a measured RCS of the RFID tag was used, the detection distance was 9.8 m for a reader sensitivity of 65 dBm and 4.7 m for a tag sensitivity of 11 dBm. Using a commercially available tag chip, the range test resulted in 4.3 m, which is compatible with the derived range equations. The tag antennas having lower Q-factors (77+j100 Omega and 55+j155 Omega) have also been fabricated, and their measured read ranges were 2.6 and 1.1+m, respectively.     

差分吸收光谱法在线测量排放烟气浓度研究

介绍了差分吸收光谱(DOAS)在线测量系统,分析了DOAS的光谱处理方法.研究了SO2气体浓度的DOAS测量方法,可以实现排放烟气中SO2的在线测量.DOAS法利用数学方法将吸收光谱分解成快变和慢变部分,他利用快变部分计算气体成分的浓度,这使得烟尘干扰和光源强度变化不影响烟气浓度测量精度.DOAS法用线测量代替点测量,可获得区域内更具有代表性的数据,能更准确的反映烟气排放情况;可同时对多种污染物的进行定性、定量分析;是非接触性测量,无需采样.     

提高脉冲LD测距系统测距能力的一种方法

从激光测距机的噪声构成分析入手,寻求提高脉冲 LD 测距机测距能力的方法。脉冲 LD测距系统的噪声主要包括热噪声、散粒噪声、背景噪声、暗电流噪声及放大器噪声。在一定的光功率、暗电流情况下,LD 测距的测距能力更容易受背景噪声的影响。研究表明,LD 测距系统中探测器偏压的变化只补偿温度变化,由此提出,在背景光照射较强时让背景噪声参与偏压调整从而抑制背景噪声的方案。实验结果证实,强背景下的信噪比提高 1 倍以上,测距能力提高 1 倍。     

陆地靶场声定位系统布站图形优化方法

提出了一种度量布站阵形结构优劣的方法.介绍了声源定位原理及解算模型,并给出了布站阵形结构优劣的度量计算公式,最后,通过计算仿真数据和试验数据验证所提方法的有效性和可行性.结果表明:图形结构的优劣程度受布站阵形和探测器数量两方面影响,文中的方法可以准确度量布站阵形结构的优劣,可为布站方案设计提供理论依据.     

FTIR spectroscopy and physical properties of an epoxy/bismaleimide IPN system

Blends of a tetrafunctional epoxy resin and a thermosetting bismaleimide (BMI) resin cured with 4,4-diamino diphenyl sulfone were investigated. Information on the conversion ofthe reactive groups upon curing was obtained by Fourier transform infrared spectroscopy. Dynamic-mechanical tests carried out on both dry and wet samples indicated the formation of an IPN-like structure and a considerable reduction of the plasticizing effect of the water absorbed in the presence of BMI. Sorption measurements at 70 °C revealed a reductionof the equilibrium water uptake with respect to the neat epoxy matrix, and a slight increase of the apparent diffusion coefficient. Furthermore, the presence of BMI enhanced such properties as the flexural elastic modulus and the compressive yield stress while reducing slightly the fracture parameters KIc, and GIc (critical stress intensity factor and critical strain energy release rate, respectively), as a consequence of the reduced ability of the IPN network to be plastically deformed under loading. © 1998 Kluwer Academic Publishers     

Optical system for tablet variety discrimination using visible/near-infrared spectroscopy

An optical system based on visible/near-infrared spectroscopy (Vis/NIRS) for variety discrimination of ginkgo (Ginkgo biloba L.) tablets was developed. This system consisted of a light source, beam splitter system, sample chamber, optical detector (diffuse reflection detector), and data collection. The tablet varieties used in the research include Da na kang, Xin bang, Tian bao ning, Yi kang, Hua na xing, Dou le, Lv yuan, Hai wang, and Ji yao. All samples (n=270) were scanned in the Vis/NIR region between 325 and 1075 nm using a spectrograph. The chemometrics method of principal component artificial neural network (PC-ANN) was used to establish discrimination models of them. In PC-ANN models, the scores of the principal components were chosen as the input nodes for the input layer of ANN, and the best discrimination rate of 91.1% was reached. Principal component analysis was also executed to select several optimal wavelengths based on loading values. Wavelengths at 481, 458, 466, 570, 1000, 662, and 400 nm were then used as the input data of stepwise multiple linear regression, the regression equation of ginkgo tablets was obtained, and the discrimination rate was researched 84.4%. The results indicated that this optical system could be applied to discriminating ginkgo (Ginkgo biloba L.) tablets, and it supplied a new method for fast ginkgo tablet variety discrimination.     

A combined preprocessing method for UHF PD detection based on kurtosis features

Abstract

Ultra-high-frequency (UHF) partial discharge (PD) detection has been proved as a powerful tool to evaluate the status of electrical equipment. Unfortunately, on-site UHF detection suffers from intensive noise interference and great computational burden, which have long been the key bottleneck for its wide utilization in the field environments. In order to provide more valuable information for subsequent processing like PD location, pattern recognition, or severity assessment, a combined preprocessing method for UHF PD detection is proposed in this paper. This scheme integrates a novel Ensemble Empirical Mode Decomposition-based signal reconstruction method and a kurtosis-based pulse window extraction method. To demonstrate the effectiveness of the presented technique, both simulated and laboratory measured PD data are obtained and further tested. Results reveal that this preprocessing method can accurately detect and extract the PD pulse from raw data, which may lessen the computational burden for any further processing. In addition, more accurate and reliable feature information can be retained.     

时延/时延差组合定位模型抗距离模糊技术研究

基于时延测量的水声跟踪定位系统,当信号传播时延大于脉冲重复周期时,就会出现测距模糊。测距模糊是高帧率定位系统不可避免的问题。研究了基于时延测量的合作声信标定位系统中的抗距离模糊问题,提出了一种新的抗距离模糊技术,基于时延测量定位模型和时延差测距模型,推导了相应的软件抗模糊算法。该方法将两种定位模型的优点相结合,实现了无模糊的、高精度的水下定位。最后海试结果验证了算法有效性和可靠性。该算法不仅具有硬件抗模糊无法具有的优点,而且与以往的硬件、软件抗距离模糊算法相比,有更灵活的运用空间。     

Thin-cell sub-Doppler spectroscopy by spatially separated beam method and pump-probe method

We experimentally demonstrate two methods that improve the resolution of sub-Doppler spectroscopy using a 1 mm thick vapor cell. The linewidths of the observed spectra are approximately 1 order of magnitude narrower than the Doppler width. The first method involves using a 1 mm thick cell filled with Rb atomic vapor and two spatially separated laser beams. By employing the same principle, we also demonstrate that it is possible to achieve the same resolution by using the pump and probe pulses of a single beam. The latter method enables us to construct a simple and robust optical setup for sub-Doppler spectroscopy.